Anti Bag Snatching Alarm

Here is a very simple as well as very useful project anti bag snatching alarm, used in bag or suitcase in order to prevent from snatching. The sound produced by anti bag snatching alarm is like police horn to get attention of people when someone attempt to snatch your bag or suitcase.

Circuit Description of anti bag snatching alarm

The heart of this entire circuit anti bag snatching alarm is operational amplifier IC CA3140 (IC1), configured as a comparator. The two inputs (inverting and non - inverting) is given to pin no 3 and 2 of operational amplifier respectively and output is obtained from pin no 6. Here IC2 (timer IC NE555) is used as monostable multivibrator. The timing component of anti bag snatching alarm is R5, VR1, and capacitor C2 with the given value in this circuit diagram lets the time of timer is about 1 minute.

For audio section, IC3 is used as alarm tone generator with an inbuilt oscillator. Finally the output is obtained from pin no 3 of IC3 and amplified by transistor T1 in order to get desire level and lastly fed to loudspeaker for output.


Resistors (all ¼-watt, ± 5% Carbon)

R1, R2, R3 = 100 KΩ

R4, R6 = 10 KΩ

R5 = 10 MΩ

R7 = 330 Ω

R8 = 220 KΩ

R9 = 1 KΩ

VR1 = 10 MΩ


C1, C3 = 0.0047 µF

C2 = 4.7 µF/16V

C4 = 0.01 µF


IC1 = CA3140 (operational amplifier)

IC2 = NE555 (timer IC)

IC3 = UM3561 (complex ROM with an inbuilt oscillator)

T1 = BD139

ZD1 = 3.3V 500mA


SW1 = ON/OFF switch

L1 = speaker 8Ω 1W

Mono plug, mono jack 8

Leave a Reply

Your email address will not be published. Required fields are marked *