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Burglar Alarm Logic

GCSE45-60 minutesLogic Gate Playground

Teacher overview

Prior knowledge: Learners should know the basic behaviour of AND, OR and NOT gates.

Learning objective: Build and explain a truth table and simple circuit for an alarm scenario.

Starter

An alarm should sound if the door opens while the system is armed. Which inputs are needed?

Main task

  1. Define input A as Armed and input B as Door open.
  2. Complete the truth table for A AND B.
  3. Build the circuit in Logic Gate Playground.
  4. Explain why OR would be unsafe for this basic alarm.
  5. Add input C as Window open and design an alarm that sounds when Armed AND (Door open OR Window open).

Support prompts

  • AND means both conditions must be true.
  • OR means at least one condition is true.
  • Write the real-world meaning beside each input.

Challenge

Add a NOT gate so the alarm only works when Maintenance mode is off.

Plenary or exit question

What is the difference between a correct truth table and a useful real-world system?

Related tool

Open Logic Gate Playground