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This circuit can be used as an anti-theft alarm. It can be placed inside a bag, on door, or windows. If the magnetic looses its contact, the SW1 will open and then the circuit will start oscillating to sound loud alarm. Here is the circuit schematic diagram : A complementary transistor-pair which is wired as [...]

The following magnetic reed switch alarm is made to be a home and handbag alarm that can be put on door on home windows, or put it inside a bag. A reed switch and a magnet form this circuit. SW1 opens whenever the magnet looses its contact with the reed switch. The circuit then starts [...]