Commercial burglar alarms consist of complex electronic components that must be serviced and repaired by professionals. However, you can demonstrate the principles behind these devices with a very simple type of burglar alarm. One form of this device consists of an electrical circuit with a buzzer that closes when a window is opened. You can complete this project with some common household items and a few special purchases.
Cut a length of wire that will reach from the battery holder to the buzzer and strip the insulation from the ends of the wire. Connect one end to the negative terminal in the battery holder and the other end to the negative buzzer terminal.
Strip the insulation from the ends of two more lengths of wire. Connect one length of wire from the positive terminal of the battery holder to a thumb tack. Connect the other length of wire from the positive buzzer terminal to another thumb tack.
Press each thumb tack through the arms of the clothes pin so that the flat ends will touch when the clothes pin is closed. Place the battery into the battery holder and the buzzer should sound unless you hold the clothes pin open.
Wrap electrical tape around all the bare wires in the circuit to prevent them from touching and creating a short circuit.
Place the open ends of the clothes pin under a window and close the window as much as possible. This should hold the clothes pin open and prevent the thumb tacks from touching to complete the circuit. If you open the window, the clothes pin will close and the buzzer will sound.