Door Opening Alarm (Hall Sensor)

Description

This simple Kit door-opening alarm uses a hall sensor to produce sound when someone opens the door. The circuit can be installed at a workshop, office, or home for security purposes. The 3-terminal hall sensor is easily available in the market. When the door is closed, neither the buzzer sounds nor LED glows. But when the door is opened, the buzzer sounds and LED glows.

Hall sensor MH183 is a magnet-operated solid-state sensor. When the magnet is brought near the sensor, its output goes low. This low output is amplified by the NPN transistor. NPN transistor inverts the operation. The magnet should be fitted on the moving part of the door and the sensor at the door frame. When the door is closed, the magnet comes close to the sensor and the alarm is off. But when the door is opened, the alarm makes a sound. The Door Opening Alarm Sensor buzzer can be replaced with a 5V relay to control a mains alarm.