This motion detector alarm circuit can detect a moving person from a distance of 1 meter. It uses a Dual IR Transmitter-Receiver module HOA1405.When the sensor detects the reflected IR rays, Alarm will sound for 2 minutes. The circuit can be modified for various applications including AC operated alarm systems.

Imagine the Panic situation in the Midnight when an intruder tries to break into the house. This Alarm will help you with its loud Police siren to abort the attempt of intrusion. With a single clap, the circuit generates the alarm for three minutes and then goes off. This is sufficient to catch the attention of neighbours.

This circuit generates inaudible ultrasound to make a barrier across the entry. At the moment the circuit detects a break in the sound barrier, it generates a loud alarm indicating the entry of a person. This can be used to protects the entry passages and helps to detect unauthorized entry of persons in protected areas.

This simple fake car alarm or alarm decoy circuit device will simulate the presence of a burglar alarm in automobiles or homes. It has a few components, uses LM3909 and is easy to build. Mount R1 where daylight can fall on it. You may change the capacitor value for different flashing rates.
During darkness, LED1 flashes, making potential intruders think an alarm system is installed.