: Category: Alarm Circuits

Touch Alarm Circuit

This circuit uses a touch sensor to trigger an alarm through a 555 timer and a transistor–relay driver stage.

When a signal is received from the touch sensor, the 555 timer generates a short output pulse. This pulse drives a transistor, which in turn activates a relay (RELE) connected to the alarm or any external load.

The system provides a simple and reliable way to detect human touch and can be used for security alarms, door entry systems, or interactive projects.

Touch Alarm Schematic

touch alarm PCB

Components

R1-100K
R2-4K7
R3-10M
R4- *SEE NOTE
R5- *SEE NOTE
P1-100K
D1-1N4148
LED1-LED2 - 3mm
C1-47uF
IC1-555
T1-2N2222 or 2N3904
RELE 6V-12V

*Note: If voltage=9V R4-390 R5-390, If voltage=12V R4-1K R5-1K