This electronic device is designed to alert the user to an intrusion. The project consists of a sensor and a control unit which are connected to each other. The [[wysiwyg_imageupload::]]sensor detects the interruption whenever an object or person comes between its transmitter and receiver. This interruption results in a signal generation which is supplied to a speaker. This way whenever an intrusion takes place, the speaker goes on. Such devices are installed at various locations in houses or offices, especially near doors, windows.In this project, the transmitter part of the circuit is an Infrared (IR) Led which transmits continuous IR rays to be received by IR receiver. The reception of rays at IR receiver results in high voltage at the output. The output of this IR sensor remains low when no signal is received. Keep on reading to find out how the circuit is constructed and what makes it work.