What happens to the door/window contact sensor when the door or window is opened?

When a door or window contact sensor is installed, it typically consists of two parts: a magnet and a switch. The magnet is placed on the door or window, while the switch is placed on the frame. When the door or window is closed, the magnet creates a magnetic field that keeps the switch closed, which allows the circuit to remain complete without triggering the alarm.

However, when the door or window is opened, the magnet moves away from the switch, breaking the magnetic field. This action causes the switch to open the circuit, which can send a signal to the alarm system that the door or window has been breached. Consequently, this broken circuit triggers the alarm, notifying property owners or monitoring services of a potential unauthorized entry.

Thus, when the door or window is opened, the correct outcome is that the circuit is broken, leading to the activation of the alarm system.