Warble-tone alarm
The circuit generates a warble-tone alarm signal that simulates the sound of a British police siren. IC1 is wired as an alarm generator and IC2 is wired as a 1 ...
Wailing alarm
This circuit simulates the sound of an American police siren. IC2 is wired as a low frequency astable that has a cycling period of about 6 seconds. The slowly v...
Receiver monitor
The alarm plugs into the earphone jack on a receiver. Then when a signal (normally fed to the headphones) is detected and applied to the gate of SCR1, it conduc...
Field disturbance sensor-alarm
The change in ambient light triggers the alarm by changing resistance of LDRl and LDR2.
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Proximity alarm
Inverters Ula and Ulb are connected in a simple RC oscillator circuit. The frequency is determined by the values of Rl, Cl, C2; and the internal characteristics...
Low-volts alarm
This inexpensive dc supply-voltage monitor sounds a warning when the voltage falls below a preset value. It is ideal for monitoring rechargeable batteries since...
Photo alarm
LDR1, a cadmium sulphide (CDS) photoresistive cell is used as the lower leg of a voltage divider between Vcc and ground. The timer terminals 2 and 6 are connect...
Door open alarm
Door open alarms are used chiefly in automotive, industrial, and appliance applications. This type of circuit can sense the opening of a refrigerator door. When...
Rain warning beeper
One small spot of rain on the sense pad of this bleeper will start this audio warning. It can also be operated by rising water. The circuit has two transistors,...
Solid-state electric fence charger
A touch-sensing circuit keeps the high-voltage generator cut off until something touches the fence wire. Contact with the fence sensing circuit wire starts the ...
Electric fence charger
Any good power transistor can be used in this circuit. The base resistor should be adjusted to obtain a pulse rate of about 50 pulses per minute. The range of v...
Electronic combination lock
When button S12 (#) is pressed, a positive voltage fed through Rl appears at the base of transistor Ql, turning it on. When Ql is conducting, pin 1 of Ul is bro...
Three-dial combination lock
Here's an effective little combination lock that you can put together in one evening's time. To open the lock, simply dial in the correct combination on the thr...
Car Ice ararm circuit
The circuit uses a thermistor and three sections of a LM3900 quad op amp IC. When the temperature drops to 36°F the LED indicator flashes about once each sec...
Light Alarm
This is a simple Photo-sensing circuit. When light hits the photo-transistor, triggers the 4011 that drives a loudspeaker. ...
Car alarm circuit using 555 timer
555 timer produces a guaranteed delay, allowing the driver to deactivate the alarm and the elimination of a control switch vulnerable outside....
House Alarm Loop Circuit
This circuit offers open and closed loop contacts (switches 1,2,3) that triggers the alarm ON and stays ON for 5 -10 minutes. The trigering delay (entrance/exit...
Car Alarm Security Circuit
This car alarm circuit offers 18 seconds delay for the entrance and the exit. It sound continually for 6 minutes and automaticaly turns horn off and gets ready ...
Simple House Alarm circuit
This house alarm circuit has open and closed loop sensor and has self shutdown function. The delay after trigering can be adjusted from 1 minute to 12. The dela...
Clever Car alarm circuit
When this car alarm circuit is activated it stays activated for 80 seconds. It has 15 seconds delay for the driver to enter and deactivate. and All timmings can...