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Shift alarm using 555

Published on Mar 02 2011 // 555 Alarm circuits

Shift alarm using 555

This Shift alarm using 555 can be used for security purposes. It can be connected to doors and windows, which when opened by a stranger, alarms. Can be used in banks, garages, lockers for security purposes.

Main Components: 

In the circuit, the main components are,

*A magnet ZT,
*A Normally Opened reed switch or magnetic switch JA,
*1A,50V SCR,
*IC555 which serves as an Astable Multivibrator
*Loud speaker.


The circuit operation is as follows. Consider a door which is connected with a magnet on the movable end. The other end of the door is connected with a Normally Opened reed switch.

When the magnet is moved, or else magnet is shifted, the reed switch contacts closes. So, it triggers the SCR through D1. When the SCR triggers, it triggers the IC555. Now, the IC555 starts to work in astable mode. The output of 555IC is given to the loud speaker. When the IC555 starts to give pulses, the Loud Speaker sounds. The frequency of the pulse may be varied using the formulae given below the circuit.