Alarm doors predominantly work using a contact sensor system, often relying on a simple yet effective reed switch and magnet mechanism.
Here's a breakdown of how it works:
-
The Core Components: Alarm door systems typically consist of two key components:
- A Reed Switch: This is a small, sealed glass tube containing two ferrous metal reeds. When a magnetic field is present, the reeds close, completing an electrical circuit.
- A Magnet: This provides the magnetic field necessary to activate the reed switch.
-
Closed Door State: When the door is closed, the magnet is positioned close to the reed switch. The magnetic field from the magnet causes the reeds inside the switch to attract each other and close, completing the electrical circuit. This "closed" circuit signals to the alarm system that the door is secure.
-
Open Door State & Alarm Trigger: When the door is opened, the magnet moves away from the reed switch. The magnetic field weakens, and the reeds spring apart, breaking the electrical circuit. This "open" circuit signals to the alarm system that the door has been opened, triggering the alarm. This trigger can activate a siren, send a notification to a monitoring station, or initiate other security protocols.
-
Simplified Explanation:
- Closed: Magnet present = Circuit closed = No Alarm.
- Open: Magnet absent = Circuit open = Alarm.
-
Variations: While the reed switch/magnet system is common, other types of sensors can also be used, including:
- Contact sensors: Basic physical contact sensors that break a circuit when the door is opened.
- Wireless sensors: These communicate with the alarm panel wirelessly.
- Vibration sensors: Detect forced entry attempts by sensing vibrations.
-
Placement: The magnet and reed switch are strategically placed, usually on the door frame and the door itself, so that they are in close proximity when the door is closed.
-
Tamper Resistance: More sophisticated systems include tamper-resistant features. For example, if someone tries to remove the sensor or magnet, it can also trigger the alarm.
