Fire alarms operate according to the same principles as burglar alarms. They need a signal such as a buzzer, a power supply to run the signal, and a trigger to activate the signal. The key difference between a fire alarm and a burglar alarm lies in the trigger. While a burglar alarm is activated when someone passes a specific barrier, a fire alarm is activated when the temperature in the surrounding area reaches a specific point.
Strip the insulation off the ends of the wire. Connect one to each of the four terminals in the battery and the buzzer.
Connect the battery and the buzzer to the piece of plywood with tape or glue. They should be close enough to connect the wires but far apart enough to place the alligator clip comfortably between them.
Wrap the wire from the positive (+) battery terminal around the top jaw of the alligator clip. Then wrap the wire from the positive (+) buzzer terminal around the bottom jaw of the alligator clip. The two wires should come into contact when the clip is closed.
Wedge the piece of wax between the jaws of the alligator clip. The wax needs to remain firmly in place when you take your hand away.
Position the alligator clip on the plywood between the battery and the buzzer, and secure it in place with tape or glue.
Connect the wires from the negative (–) terminals on the battery and the buzzer. During a fire, the wax will melt, which will close the jaws of the alligator clip and complete the circuit. The alarm will then go off.
Place the fire alarm in an appropriate place in your home.