Simple Multidoor Opening Alarm with Indicator
This door-opening alarm alerts you of intruders . You can use it for up to three doors. You simply need to fit a small unit including reed switch on each doorframe and fix a magnet on the moving door such that the magnet aligns with the reed switch when the door is closed. A separate unit incorporating the power supply, three LEDs and a buzzer is to be kept by your side inside your room. A three-core ribbon cable from this unit goes to each door unit. One core goes to the positive terminal, second to the negative terminal and third to the output of the unit. When the door is closed, the reed switch terminals are shorted and the alarm does not sound. Multidoor Opening Alarm with Indicator Circuit Diagram When door 1 is opened by someone, transistors in the corresponding door unit conduct and the buzzer sounds. LED1 glows to indicate opening of door 1. Due to diode latching action, the alarm will sound continuously even after the door is closed. It can be stopped only by pressing th...