Building an alarm circuit is one of the easiest circuits to make. There are two type types of alarm circuits: a closed-circuit system and an open-circuit system. Here are the steps to construct a closed-circuit system alarm.
Prepare your wires. For the circuit to have clean contacts, you’ll need to peel off the wire insulation at the end of the wires. Peel off ½ inch of insulation for the wire ends that will attach to the battery. Peel off 1 inch of insulation for the wire ends that will attach to the clip.
Connect the buzzer to the switch. In a closed-circuit system, the only time the alarm will not ring is when the circuit is broken. This means that whenever the electric current is moving along a continuous route, the alarm will sound. Start out by attaching one piece of wire to one of the buzzer terminals. Attach the other end of the wire to one prong of the clip by wrapping the wire around the prong tip.
Connect the switch to the battery. Take a second piece of wire and wrap the end around the second prong on the clip. Make sure the wires are touching when the clip is closed. This is the part of the circuit that opens and closes. Connect the other end of this wire to one of the battery terminals.
Connect the battery to the buzzer. At this point, you might want to stick a thin piece of plastic, or cardboard inside the clip to keep the wires from touching. Otherwise, the buzzer will keep ringing once the battery is connected to it. Take the third piece of wire and connect an end to the other battery terminal. Connect the other end of this wire to the remaining terminal on the switch.
Your circuit is complete. Pull the cardboard piece out of the clip, and the buzzer should go off. If the buzzer doesn’t go off, check your battery terminal and buzzer terminal connections. Also make sure the clip wires are touching when the clip is completely closed.
Make sure your battery source is strong enough to power the buzzer, but not so strong that it burns the buzzer out.
Use a plastic clip or a metal clip with plastic ends to avoid getting shocked by the current.