This type of sensors is often used on doors to apartment buildings and secure areas in government offices. In a closed circuit system, when the door is closed, the magnet pulls the metal switch closed so the circuit is complete. The current powers the relay’s electromagnet, so the buzzer circuit stays open. When you move the magnet by opening the door, the spring snaps the switch back into the open position. This cuts off the current and closes the relay, sounding the alarm.

Of all the sensors used in a home security system, magnetic sensors are the simplest and cheapest. Typical magnetic sensor in the market has a small operating gap and though it may work fine for most doors and windows in a home, it does not cut it for larger doors. Larger door such as the garage door uses a different type of sensor such as the 7113-10 TEN-PACK OF 7113 MAGNETIC CONTACT SWITCHES because of the size of the opening. This type of sensor is commonly available and here are some of the links to where you can get one.

Related posts:

1. Understanding How Alarm Systems Work
2. Sensors for home security systems
3. Glass break sensors for home security systems