R07-U3 · usually age 7 · Little Inventors

Signals and Switches

How can a machine communicate?

Pilot unit plan · 4 sessions · not yet classroom-validated

Build: Low-voltage signal model

How a machine can communicate: an input (a switch) makes an output (a light or a sound). Children play a signal game, then at the adult's station snap together a loop of plastic modules from a kit made for their age (Snap Circuits Beginner (Elenco, SCB20)), see that the light works only when the loop is closed, and send signal patterns that mean help and OK.

Sense
Act
Power and safety

Who it is for

Age is a starting point, never a limit. A learner who can show what this unit starts from can begin here at any age.

How they learn: By making, moving and playing: ramps, wheels, levers, a classmate acting as a robot. Pictures and arrows instead of words; no code text.
The adult's role: An adult leads every session and prepares anything powered. Children never handle loose batteries, sharp tools or hot parts.
Session: 45–60 minutes
Hardware: No controller needed: cardboard, wheels, gears; optional enclosed low-voltage modules. The adult prepares or checks any wiring. No loose batteries, coin cells, small magnets, sharp tools or hot parts.

Starts from

Safe making
Follow safe-making rules: tools, small parts, hands clear of moving parts.
Built in R06-U1 Machines Around Us
Predict and test
Predict what will happen, test it, and say what happened.
Built in R06-U1 Machines Around Us

Builds, and what it is the input for

Closed circuits
Build a safe low-voltage circuit and say why it must be a closed loop.
Input for R10-U1 Power a Moving Machine, R12-U1 Safe Circuits and Power
Switch inputs
Use a switch or touch as an input to a machine.
Input for R08-U1 Input, Output and Events, R08-U3 Robots That Respond, R09-U2 Sense the World, R12-U2 Arduino as a Controller
Outputs
Make a machine respond with a light, a sound or a movement.
Input for R08-U1 Input, Output and Events, R08-U2 Make It Move with Blocks, R10-U1 Power a Moving Machine, R10-U3 Create an Automatic Response, R12-U1 Safe Circuits and Power

In the studio today

No studio lab or activity for this unit yet.

Sessions

Session 1 · 45 min
How can a machine talk without words?
A signal is a message without words: a light, a sound or a movement that means something. The input is what we do (press a switch); the output is what the machine does (light up, beep). A closed loop: the message goes all the way round.
The adult says first: “A machine can talk with a light or a sound. Let's play signals.”
Picture cards for the children (symbols and drawings; they read nothing)
1. ✋ ⬇ — picture: a hand pressing a switch: the input
2. 💡 — picture: a light shining: the output
3. • • • — picture: three short claps: help
4. ▬ — picture: one long hand-raise: OK
5. ◯ — picture: children in a closed circle holding hands
6. ✋ ⛔ 🔋 — picture: only the adult touches the battery box or power link
7. ⏻ ⛔ — picture: power off before changing anything
Key words (said aloud, pointing to the card): input · output · signal
Timing (0 of 45 min at the screen)
1. 10 minAway from the screen: The signal game: the switch card and the light child.
2. 10 minAway from the screen: The class's signal code: three short for help, one long for OK.
3. 15 minAway from the screen: The loop game: the squeeze goes round and back; one child lets go.
4. 10 minAway from the screen: The adult shows the closed kit box and its safety cards.
In the studio
No studio lab: this session is off-screen.
Hands-on
Nothing is powered. The signal game: one child is the switch and holds up the press card; the partner is the light and raises a hand only while the card is up. Then the class's signal code, two picture cards: three short claps mean help, one long hand-raise means OK. The loop game: the group sits in a circle holding hands, and the adult, who is the battery, starts a gentle squeeze that passes from hand to hand all the way round and back to the adult. The light child raises an arm only when the adult feels the squeeze come all the way back and nods. Then one child lets go of a hand (the switch opens): the squeeze cannot come back, so the arm stays down. Try the gap on both sides of the light child, before it and after it: the arm stays down both times. If any child cannot or would rather not hold hands, the circle passes a beanbag from hand to hand instead, never a looped rope. It is a game that shows the path must go all the way round, not how electricity really moves. Last, the adult shows the closed kit box and its safety picture cards, and the children copy each rule with their hands.
Evidence to collect
The adult's note of which children made the help and OK signals and said what the input and the output were in the game.
Predict
Before a child lets go in the loop game, everyone points: will the light child's arm go up or stay down?
Debug
If the light child's arm goes up with the loop open, start again slowly and follow the squeeze round: where did it jump the gap?
Reflect
What was the input in our game, and what was the output?
⚠ Adult checks: The kit stays closed in the adult's box: this session only shows it. The beanbag, if used, is soft, at least 6 cm across and its seams are checked by the adult; no rope or string is looped.
Works towards: Switch inputs, Outputs
Session 2 · 50 min
Why must the path go all the way round?
A closed loop: the light works only when the path goes from the battery holder through the switch and the light and back again. The slide switch opens and closes the loop. The children snap the modules together with the power off; only the adult snaps the power link on, and unsnaps it.
The adult says first: “Snap the parts into a loop. Then the adult adds the power link.”
Picture cards for the children (symbols and drawings; they read nothing)
1. ◯ 💡 — picture: a closed loop with the light shining
2. ◠ ✗ — picture: a loop with a gap, the light dark
3. ⏻ — picture: the slide switch, on and off
4. 👀 ✓ — picture: the adult checking the loop with a finger
5. 🔗 ✋ — picture: the red power link in the adult's hand
6. ✋ ⛔ 🔋 — picture: only the adult touches the battery box or power link
7. ⏻ ⛔ — picture: power off before changing anything
Key words (said aloud, pointing to the card): loop · switch · closed
Timing (0 of 50 min at the screen)
1. 10 minAway from the screen: The safety cards again; the adult shows the modules, the power link and the loop card.
2. 25 minAway from the screen: Each pair snaps the loop with the power link off; the adult checks it and snaps the link on; switch on and off.
3. 10 minAway from the screen: The gap: guess, then switch on. Why does it stay dark?
4. 5 minAway from the screen: The adult photographs each loop, the build only, unsnaps the power link and takes the cells out.
In the studio
No studio lab: this session is off-screen.
Hands-on
At the adult's station, up to six children, one pair at a time at the kit. Before the session, away from the children, the adult puts 3 AA alkaline cells in the battery holder, screws its cover shut, fixes the holder on the grid and makes its other connection, with the power link off: the power link is the one 3-snap wire that joins the holder to the loop, marked with red tape and kept in the adult's hand. Spare modules and wires stay in the adult's box, and no metal tools or objects are on the kit table. With the power link off, each pair snaps a loop onto the base grid with the slide switch off, copying the adult's picture card of the maker's Project 4 (Red Light): the slide switch, the LED and 3-snap wires, the LED's + mark as on the card. The adult checks the loop, then snaps the power link on, last, and stays within arm's reach of it. A child slides the switch on: the light shines; off: it goes out. Then, with the power link off again (the adult unsnaps it first), the adult takes one wire out, leaving a gap, and the children guess. The adult checks the loop and snaps the power link back on, and a child slides the switch on: no light. The adult unsnaps the power link before the next pair. At the end the adult unsnaps the power link, takes the cells out and shuts the kit in the adult's box.
Evidence to collect
A photo of each pair's closed loop and of the loop with its gap (the build only), and the adult's note of what each child said about why the light went out.
Predict
Before each switch-on, every child holds up the light card or the dark card: will it shine?
Debug
If the light stays dark in a closed loop, the adult unsnaps the power link, checks every snap is pressed home, the LED's + mark and the loop against the card, and tries again; then the adult replaces all three cells together.
Reflect
Why does the light need a path all the way round?
⚠ Adult checks before power-on: Cells: 3 AA alkaline, as the maker says, all three replaced together. Only the adult puts them in, away from the children, and screws the holder's cover shut. Children never touch a cell or the holder. The adult fixes the battery holder on the grid before the session and makes its other connection. Children snap only the parts on the card, never onto the holder or the power link's place. The power link (a planning choice): one 3-snap wire marked with red tape, the only way power reaches a loop. Only the adult snaps it on, last, and unsnaps it first, before any change. Power off to change anything: the adult unsnaps the power link before any part is added, moved or taken away. Children never change a loop that has power. Before the power link goes on: spare modules and wires back in the adult's box, no metal tools or objects on the kit table, and the adult within arm's reach of the power link. Before the power link goes on, the adult checks: only the parts on the card; every path from the holder goes through the light or horn; no wire or switch across the holder, the light or the horn. Then: the light's and the horn's + marks as on the card, every snap pressed home, any slide switch off. Only then does the adult snap the power link on, last. Short circuits, the maker's two examples: a 3-snap wire straight across the holder, and a circuit whose slide switch, turned on, makes a path that skips the light or horn. The loop check looks for both. Never left with power: if the adult steps away, the power link comes off first. At the end of every powered session the adult takes the cells out and shuts the kit in the adult's box. If anything gets warm, smells or cracks: hands off and tell the adult, who unsnaps the power link. A cracked or broken part leaves the kit; the adult gets a replacement from the maker.
Works towards: Closed circuits, Switch inputs, Outputs
Session 3 · 50 min
Which switch can send a signal?
Two kinds of switch: the slide switch stays where it is put; the press switch closes the loop only while it is pressed. A press switch can make a pattern of short and long. The horn is a second output.
The adult says first: “Press and hold: light on. Let go: light off. Now make patterns.”
Picture cards for the children (symbols and drawings; they read nothing)
1. ⏻ ➡ — picture: the slide switch staying on
2. ✋ ⬇ 💡 — picture: pressing the press switch: light on
3. • • • — picture: three short flashes: help
4. ▬ — picture: one long flash: OK
5. 🔊 ▭ — picture: the horn under a folded cloth
Key words (said aloud, pointing to the card): press · pattern · signal
Timing (0 of 50 min at the screen)
1. 10 minAway from the screen: The safety cards; the adult shows the press switch and the covered horn.
2. 20 minAway from the screen: Each pair snaps the press-switch loop with the power link off; press and let go.
3. 15 minAway from the screen: The covered horn, a warning before each beep: short beeps and a slightly longer one; then the code with the light.
4. 5 minAway from the screen: The adult photographs a loop, the build only, unsnaps the power link and takes the cells out.
In the studio
No studio lab: this session is off-screen.
Hands-on
At the adult's station, one pair at a time at the kit. Before the session, away from the children, the adult puts 3 AA alkaline cells in the battery holder, screws its cover shut, fixes the holder on the grid and makes its other connection, with the power link off: the power link is the one 3-snap wire that joins the holder to the loop, marked with red tape and kept in the adult's hand. Spare modules and wires stay in the adult's box, and no metal tools or objects are on the kit table. With the power link off, each pair snaps their light loop from the adult's card with the press switch in place of the slide switch; the adult checks the loop, snaps the power link on and stays within arm's reach of it. Children press and let go: the light shines only while the switch is pressed. Then, with the power link off again, the adult swaps the light for the horn, making the maker's Project 6 (Horn): the press switch, the horn and 3-snap wires, covers the horn with a folded cloth and checks the loop before snapping the power link back on. The adult says when a beep is coming, before each one; children make short beeps and one slightly longer one, still short, and any child may choose the light instead and sit the horn out. With the power link off again, the adult swaps the horn back for the light, checks, then snaps the power link on, and the pairs practise the class code: three short for help, one long for OK. The adult unsnaps the power link before the next pair. At the end the adult unsnaps the power link, takes the cells out and shuts the kit in the adult's box.
Evidence to collect
The adult's note of which children made a help pattern and an OK pattern with the press switch, and a photo of the press-switch loop (the build only).
Predict
Before letting go of the press switch, each child says: will the light stay on or go out?
Debug
If a pattern is hard to read, slow it down: count the presses aloud together, with a clear stop between them.
Reflect
Which switch is better for sending a signal, and why?
⚠ Adult checks before power-on: Cells: 3 AA alkaline, as the maker says, all three replaced together. Only the adult puts them in, away from the children, and screws the holder's cover shut. Children never touch a cell or the holder. The adult fixes the battery holder on the grid before the session and makes its other connection. Children snap only the parts on the card, never onto the holder or the power link's place. The power link (a planning choice): one 3-snap wire marked with red tape, the only way power reaches a loop. Only the adult snaps it on, last, and unsnaps it first, before any change. Power off to change anything: the adult unsnaps the power link before any part is added, moved or taken away. Children never change a loop that has power. Before the power link goes on: spare modules and wires back in the adult's box, no metal tools or objects on the kit table, and the adult within arm's reach of the power link. Before the power link goes on, the adult checks: only the parts on the card; every path from the holder goes through the light or horn; no wire or switch across the holder, the light or the horn. Then: the light's and the horn's + marks as on the card, every snap pressed home, any slide switch off. Only then does the adult snap the power link on, last. Short circuits, the maker's two examples: a 3-snap wire straight across the holder, and a circuit whose slide switch, turned on, makes a path that skips the light or horn. The loop check looks for both. Never left with power: if the adult steps away, the power link comes off first. At the end of every powered session the adult takes the cells out and shuts the kit in the adult's box. If anything gets warm, smells or cracks: hands off and tell the adult, who unsnaps the power link. A cracked or broken part leaves the kit; the adult gets a replacement from the maker. The horn is loud: a folded cloth over it (a planning choice), short beeps only, a warning from the adult before each beep, never near an ear. Any child may choose the light; ear defenders are offered.
Works towards: Switch inputs, Outputs, Closed circuits
Session 4 · 55 min
Can we send a signal on purpose?
An intentional signal: the child chooses a message (help or OK), says what the rescuer will see or hear, sends it with the press switch, and the rescuer answers with the matching card. The safe steps every time: power off to change anything, the adult's check before the power link goes on.
The adult says first: “Choose help or OK. Send it with the switch. Your partner answers.”
Picture cards for the children (symbols and drawings; they read nothing)
1. • • • — picture: three short: help
2. ▬ — picture: one long: OK
3. ✋ ⬇ — picture: pressing the press switch to send
4. 🙋 ▭ — picture: the rescuer holding up the matching card
5. ✋ ⛔ 🔋 — picture: only the adult touches the battery box or power link
6. ⏻ ⛔ — picture: power off before changing anything
Key words (said aloud, pointing to the card): signal · help · safe
Timing (0 of 55 min at the screen)
1. 10 minAway from the screen: The safety cards; each pair snaps its loop with the power link off.
2. 30 minAway from the screen: Send and answer: help or OK, then swap roles.
3. 10 minAway from the screen: Each child shows the safe steps with the cards.
4. 5 minAway from the screen: The adult photographs a loop, the build only, then takes the cells out and puts the kit away.
In the studio
No studio lab: this session is off-screen.
Hands-on
At the adult's station, pairs in turn. Before the session, away from the children, the adult puts 3 AA alkaline cells in the battery holder, screws its cover shut, fixes the holder on the grid and makes its other connection, with the power link off: the power link is the one 3-snap wire that joins the holder to the loop, marked with red tape and kept in the adult's hand. Spare modules and wires stay in the adult's box, and no metal tools or objects are on the kit table. With the power link off, each pair chooses the light or the horn (covered with its folded cloth) and snaps their press-switch loop from the card; the adult checks it, snaps the power link on and stays within arm's reach of it. The sender picks a message card (help or OK) without showing it, says what the rescuer will see or hear, and sends it with the press switch; the rescuer, facing away from the cards, holds up the matching picture card. Before a horn message the adult says a beep is coming, and any child may choose the light. Then the partners trade roles. Each child shows the adult the safe steps with the safety cards: power link off before changing anything, hands off the battery box and the power link, tell the adult if anything is warm. The adult unsnaps the power link before the next pair. At the end the adult unsnaps the power link, takes the cells out and shuts the kit in the adult's box.
Evidence to collect
The unit's evidence: each child shows an intentional safe signal response (chooses help or OK, says what the rescuer will see or hear, sends it with the press switch, the rescuer answers with the matching card, and the child names the safe steps), shown to the adult; kept as the adult's note and a photo of the loop on the grid, never of the child.
Predict
Before sending, the sender says what the rescuer will see or hear: three short or one long.
Debug
If the rescuer picks the wrong card, send it again more slowly; if the light or horn does not answer the switch, the adult unsnaps the power link and checks the loop again.
Reflect
Where do machines around you use a light or a sound to tell us something?
⚠ Adult checks before power-on: Cells: 3 AA alkaline, as the maker says, all three replaced together. Only the adult puts them in, away from the children, and screws the holder's cover shut. Children never touch a cell or the holder. The adult fixes the battery holder on the grid before the session and makes its other connection. Children snap only the parts on the card, never onto the holder or the power link's place. The power link (a planning choice): one 3-snap wire marked with red tape, the only way power reaches a loop. Only the adult snaps it on, last, and unsnaps it first, before any change. Power off to change anything: the adult unsnaps the power link before any part is added, moved or taken away. Children never change a loop that has power. Before the power link goes on: spare modules and wires back in the adult's box, no metal tools or objects on the kit table, and the adult within arm's reach of the power link. Before the power link goes on, the adult checks: only the parts on the card; every path from the holder goes through the light or horn; no wire or switch across the holder, the light or the horn. Then: the light's and the horn's + marks as on the card, every snap pressed home, any slide switch off. Only then does the adult snap the power link on, last. Short circuits, the maker's two examples: a 3-snap wire straight across the holder, and a circuit whose slide switch, turned on, makes a path that skips the light or horn. The loop check looks for both. Never left with power: if the adult steps away, the power link comes off first. At the end of every powered session the adult takes the cells out and shuts the kit in the adult's box. If anything gets warm, smells or cracks: hands off and tell the adult, who unsnaps the power link. A cracked or broken part leaves the kit; the adult gets a replacement from the maker. The horn is loud: a folded cloth over it (a planning choice), short beeps only, a warning from the adult before each beep, never near an ear. Any child may choose the light; ear defenders are offered. Photos are of the build only, taken by the adult on the setting's device, following its photo policy: no child in the frame, no names visible, the build on the table or floor, not in a hand. Nothing is uploaded to this studio and no name goes into it; the adult's notes follow the setting's records policy.
Works towards: Outputs, Switch inputs, Closed circuits

Materials

Per group of up to six: a big cardboard box of prepared parts (pre-cut by the adult), masking tape, glue sticks, crayons and large sheets of paper for drawings
The adult's picture cards for the session, drawn large (drawn by hand today; printable cards are planned)
One Snap Circuits Beginner (Elenco, SCB20) kit per adult station, labelled Ages 5-8, using its the mini base grid, the 3-snap wires, the battery holder (B3B), the slide switch (S1), the press switch (S2), the red/yellow LED (D10) and the horn (W1); the light motor (M7), the lamp and the egg stay in the box
The power link: the one 3-snap wire in each loop that joins the holder to the loop, marked with red tape and kept in the adult's hand
3 AA alkaline cells and a small Phillips screwdriver for the holder's cover, both kept by the adult, never in the children's reach and never on the kit table; when the cells run down, the adult replaces all three together
A folded cloth to cover the horn, and ear defenders for any child who wants them
A soft beanbag at least 6 cm across, for the loop game if the circle uses one
The adult's picture cards of each loop, drawn from the maker's Project 4 (Red Light) and Project 6 (Horn) with each + mark and the power link shown, and the class's signal-code cards

⚠ Safety before any session

Powered parts: only the plastic modules of one snap-together kit made for this age (Snap Circuits Beginner (Elenco, SCB20), labelled Ages 5-8), prepared and checked by the adult.
Cells: 3 AA alkaline, as the maker says, all three replaced together. Only the adult puts them in, away from the children, and screws the holder's cover shut. Children never touch a cell or the holder.
No coin or button cells and no rechargeable lithium cells (no Li-ion or LiPo): only the kit's own AA alkaline cells, in its screwed holder.
No mains: nothing in this unit plugs into a wall socket, and no adapter, charger or extension lead goes near the kit.
No bare or loose wires and no other parts: only the kit's own snap modules and 3-snap wires, on its base grid. Never a second battery or another power source.
The adult fixes the battery holder on the grid before the session and makes its other connection. Children snap only the parts on the card, never onto the holder or the power link's place.
The power link (a planning choice): one 3-snap wire marked with red tape, the only way power reaches a loop. Only the adult snaps it on, last, and unsnaps it first, before any change.
Power off to change anything: the adult unsnaps the power link before any part is added, moved or taken away. Children never change a loop that has power.
Before the power link goes on: spare modules and wires back in the adult's box, no metal tools or objects on the kit table, and the adult within arm's reach of the power link.
Before the power link goes on, the adult checks: only the parts on the card; every path from the holder goes through the light or horn; no wire or switch across the holder, the light or the horn.
Then: the light's and the horn's + marks as on the card, every snap pressed home, any slide switch off. Only then does the adult snap the power link on, last.
Short circuits, the maker's two examples: a 3-snap wire straight across the holder, and a circuit whose slide switch, turned on, makes a path that skips the light or horn. The loop check looks for both.
If anything gets warm, smells or cracks: hands off and tell the adult, who unsnaps the power link. A cracked or broken part leaves the kit; the adult gets a replacement from the maker.
The horn is loud: a folded cloth over it (a planning choice), short beeps only, a warning from the adult before each beep, never near an ear. Any child may choose the light; ear defenders are offered.
Never left with power: if the adult steps away, the power link comes off first. At the end of every powered session the adult takes the cells out and shuts the kit in the adult's box.
No scissors in this unit: nothing is cut, and the kit table holds only the kit's own parts.
The kit's label warns of small parts. The adult checks each piece against the small-parts cylinder and counts the kit out and back in; it stays at the adult's station.
Small parts: nothing loose, or that could come off, that fits inside the small-parts cylinder (31.70 mm wide, 57.10 mm long). No beads, marbles, buttons, small magnets or coin cells. If in doubt, leave it out.
The one exception is the kit's own pieces, which stay under the adult's count.
Photos are of the build only, taken by the adult on the setting's device, following its photo policy: no child in the frame, no names visible, the build on the table or floor, not in a hand.
Nothing is uploaded to this studio and no name goes into it; the adult's notes follow the setting's records policy.

Safety for every band

Low voltage only: battery packs or USB. Never mains electricity.
Never connect a motor straight to a controller pin: use a driver and a separate supply.
Every moving robot has a power-off switch within reach that cuts the motor battery (or all power). A software stop button is extra, never a replacement.
No coin or button cells and no loose small magnets; battery compartments screwed shut.
Guard wheels and moving parts against pinched fingers; keep robots slow and indoors.
No exposed lithium cells, improvised chargers or lasers.
No Li-ion, LiPo or RC packs: AA alkaline or NiMH cells in a closed holder with a switch, or USB.
Check polarity and voltage before power-on; a 3.3 V board must not receive 5 V signals.

Notes for the adult

Say each step aloud: your words come first. The children read nothing. Each session's picture cards show symbols and drawings only; say the key word as you point to its card.
These plans assume one adult for up to six children. The adult leads every step, prepares every cut before the session, makes every hole (by the hole rule) and keeps the craft box and the split pins.
With a whole class, run a carousel: one station of up to six children run by the adult, and independent stations within the adult's sight where the others have a defined task with no scissors, split pins or ramps (each plan's “Whole class:” note names them). Groups swap until every child has been at the adult's station.
Whole class: the kit stays at the adult's station, one pair at a time. The independent stations are drawing the class's signal code (three short, one long) with crayons, playing the signal game with the press card, and drawing a closed loop and a loop with a gap. In the powered sessions (2–4) a second adult for the independent stations is recommended, so that the kit's adult watches only the kit.
Inclusion: every child takes part. Mobility: a child can show a movement their own way (hands, arms or a large soft toy), be the robot on big, clear squares in a wheelchair, lay the cards or give the instructions, or move a large soft toy across a table-top grid. Vision: large, high-contrast or tactile picture cards (raised outlines). Hearing: say each key word and point to its card at the same time, facing the child. Left-handed children get left-handed scissors with rounded ends.
In this unit, a child who cannot hear the horn uses the light, and a child who cannot see the light uses the covered horn. A child who finds sudden sounds hard is told before each beep, may choose the light every time, and is offered ear defenders. In the loop game, a beanbag passed round the circle replaces holding hands for any child who cannot or would rather not hold hands.
Evidence is showing and telling: a demonstration, a photo of the build (never of a child, no names visible) or a drawing that you keep, or your own short note. No names in the studio, no scores, no uploads.
The CPSC's small-parts rule is written for toys for children under 3, and it exempts paper and writing materials such as crayons (16 CFR 1501.3, quoted). These plans apply its cylinder check to the loose objects children handle, and to anything that could come off, a stricter planning choice: groups mix ages and younger visitors come in. Paper and crayons stay in use; the adult collects glue-stick caps and crayon stubs at the end of each session.
No screen in this unit: every session is away from the screen. Robot Instructions has no level for it.
Why this kit: Snap Circuits Beginner (Elenco, SCB20) is a widely used snap-together kit whose maker labels it Ages 5-8. Its parts are mounted on plastic modules, its battery holder's cover comes off with a Phillips head screwdriver, and it runs on 3 AA alkaline cells that only you put in (1.5 V each, 4.5 V in all). The age label is not the whole answer: the maker also asks the adult to make sure the child “understands and follows all of the safety warnings”, which this plan does not expect of a 7-year-old. Its answer is that you hold the power: the children never touch the cells, the holder or the power link, and nothing they build has power until you have checked it. Any equivalent kit must meet the same requirements (planning choices): an enclosed battery holder with a screwed cover, parts mounted on plastic modules, snap-together or plug-together connectors, no bare wires, one wire you can use as the power link, and a maker's age label that includes 7.
Who builds what (founder decision, 2026-11-07: children snap, the adult checks): the children snap the modules together, but only while the power link is off, so nothing they build has power until you have checked it. You alone fill and close the holder, fix it on the grid, snap the power link on, last, and unsnap it first. A circuit the children only switch on would be safer still, but they could not build a loop, which is what this unit's outcome asks.
The maker's own warnings, quoted in the sources: check the wiring before turning on a circuit, never leave a circuit unattended with the batteries in, never connect other batteries or power sources, discard cracked or broken parts, and adults decide which experiments suit the child. This plan uses two of the maker's loops only.
Short circuits, in the maker's words: “Placing a 3-snap wire directly across the batteries is a SHORT CIRCUIT.” and “When the slide switch (S1) is turned on, this circuit has a SHORT CIRCUIT path (as shown by the arrows).” This plan does not rely on the kit to prevent either: your loop check looks for a wire or a switch across the holder, the light or the horn, every time. The maker also asks that the LED's and the horn's + marking be “positioned as per the drawing”, so each picture card shows its + marks.
Take the cells out at the end of every powered session: the maker says “Never leave a circuit unattended while the batteries are installed.” When the cells run down, replace all three together: the maker says “Do not mix old and new batteries.”
A cracked or broken part leaves the kit, as the maker says (“Discard any cracked or broken parts.”). You order its replacement from the maker and check it before it joins the kit; the children never handle the battery holder, whatever a replacement part's own label says.
No coin or button cells come near this unit: the rule under Reese's Law (16 CFR 1263.2, quoted) defines their ingestion hazard: one swallowed or inserted “can become lodged in the digestive tract or airways” and can potentially “cause death or serious injury”, through causes that include “electrical burns” and “pressure necrosis”. The kit's own cells are AA, which only you put in, in a holder screwed shut.
Never anything from the mains in this unit, not even to test it: the maker says “Never connect Snap Circuits® to the electrical outlets in your home in any way!”, and the HSE, writing about electricity at work, says “Electricity can kill or severely injure people”. The unit needs nothing but the 4.5 V from the cells you put in the kit's holder.
Never rechargeable lithium cells (no Li-ion or LiPo) and never a mix: the maker says to use only 1.5 V AA alkaline cells and not to mix alkaline with other kinds.
The LED module lights red one way round and yellow the other (the maker's own test); either colour can carry the class's code. The light motor stays in the box because the maker warns not to touch it during operation; the lamp and the egg are not needed.
The horn makes, in the maker's words, “an annoying sound”, and it has no volume control: covering it with a folded cloth, keeping beeps short and warning before each one is this plan's choice.
This unit relies on safe-making rules (R06-U1) and on predicting before trying (R06-U1). It does not teach them again.
Readiness decides, not age: a child who already sends a signal on purpose with a switch and a light or a sound has what R08-U1 needs from this unit.

Planned studio features

Not built yet. The unit runs without them.

Printable picture cards: input, output, the signal code, a closed loop and a gap, the slide and press switches, the power link, the covered horn and the safety cards.
A printable loop sheet: each loop drawn module by module, with each + mark and the power link, for the children to copy onto the grid.

Sources

The facts this plan relies on, in each source's own words.

US CPSC: Child Safety: Summary Information for Small Parts, 16 C.F.R. Part 1501
“A small part is any object that fits completely into a specially designed test cylinder 2.25 inches /57.10mm long by 1.25 inches /31.70 mm wide that approximates the size of the fully expanded throat of a child under three years old. … A piece of a toy or article that breaks off during testing that simulates use or abuse by children. … Toys and games that are or contain small parts as manufactured and that are intended for use by children from 3 to 6 years old must be labeled to warn purchasers not to buy them for children under 3 years old because those children could choke on the small parts. Marbles, small balls, and balloons require similar warnings.”
US eCFR, 16 CFR 1501 (a CPSC rule): Method for identifying toys and other articles intended for use by children under 3 years of age which present choking, aspiration, or ingestion hazards because of small parts
“This regulation does not apply to toys or articles which are solely intended for use by children 3 years of age or older. … The following articles are exempt from this regulation … Books and other articles made of paper; … Writing materials such as crayons, chalk, pencils, and pens; … Any components or pieces (excluding paper, fabric, yarn, fuzz, elastic, and string) which have become detached from the article as a result of the use and abuse testing shall be placed into the cylinder, one at a time.”
Elenco Snap Circuits Beginner, SCB20 (the maker's product notes: its age label, batteries, modules and warning)
“Perfect for future engineers age 5+. … Extra safety features for younger engineers, 5 and up. … Requires 3 "AA" batteries (not included) … All parts are mounted on plastic modules and snap together with ease. … No tools required. … Ages | 5-8 … Product Warning | WARNING CHOKING HAZARD - Small parts. Not for Children under 3 yrs”
Elenco Snap Circuits Beginner Instruction Manual, 753097 (the maker's product notes: warnings, parts, batteries and short circuits)
“AGES 5+ … Always check your wiring before turning on a circuit. Never leave a circuit unattended while the batteries are installed. Never connect additional batteries or any other power sources to your circuits. Discard any cracked or broken parts. … adults should exercise discretion as to which experiments are suitable and safe … Make sure your child understands and follows all of the safety warnings, and keeps them at hand for reference. … Use only 1.5V AA type, alkaline batteries (not included). … Do not mix old and new batteries. … Do not mix alkaline, standard (carbon-zinc), or rechargeable (nickel-cadmium) batteries. … Do not short circuit the battery terminals. … Batteries are harmful if swallowed, so keep away from small children. … WARNING: SHOCK HAZARD Never connect Snap Circuits® to the electrical outlets in your home in any way! … 3-Snap Wire … B3B | Battery Holder - uses 3 1.5V type AA (not included) … D10 | Red/Yellow LED … Slide Switch … Press Switch … Horn … Be sure that the light motor (M7), red/yellow LED (D10, and horn (W1) have their “+” marking positioned as per the drawing. … Do not touch the light motor (M7) during operation. … Remove the safety cover from the battery holder (B3B) with a Phillips head screwdriver. Insert three (3) 1.5V “AA” batteries (not included) into the battery holder (B3B). … Placing a 3-snap wire directly across the batteries is a SHORT CIRCUIT. … When the slide switch (S1) is turned on, this circuit has a SHORT CIRCUIT path (as shown by the arrows). … be careful not to accidentally make a direct connection across the battery holder (a “short circuit”), as this may damage and/or quickly drain the batteries. … Be sure that all connections are securely snapped. … Do the same with the LED, it should light red or yellow, depending on how you oriented it. … Do the same with the horn (horn + to battery +), it should make an annoying sound. … Project 4 : Red Light … Project 6 : Horn”
US eCFR, 16 CFR 1263.2 (a CPSC rule): Definitions, in the Safety Standard for Button Cell or Coin Batteries (Reese's Law)
“section 5 of Reese's Law … Button cell or coin battery means: … A single cell battery with a diameter greater than the height of the battery; … Ingestion hazard means a hazard caused by a person swallowing or inserting a button cell or coin battery into their body whereby: … The button cell or coin battery can become lodged in the digestive tract or airways; and … Can potentially cause death or serious injury through choking, generation of hazardous chemicals, leaking of hazardous chemicals, electrical burns, pressure necrosis, or other means.”
UK HSE: Introduction to electrical safety
“Electricity can kill or severely injure people and cause damage to property. … electric shock and burns from contact with live parts … Even incorrectly wiring a plug can be dangerous and lead to fatal accidents or fires.”