Magnetic Contact Switch – Wired

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Magnetic Contact Switch

A magnetic contact switch, often simply called a magnetic contact or door/window sensor, is a simple yet highly effective security device that detects when a door, window, gate, or any movable barrier is opened or closed.

How it Works:

It consists of two main parts:

1. The Sensor Unit (with a Reed Switch): This part contains a reed switch. A reed switch is a small, hermetically sealed (airtight) glass capsule with two tiny, flexible magnetic metal reeds (or contacts) inside. These reeds are usually made of a ferromagnetic material. This sensor unit is typically mounted on the stationary part of the opening (e.g., the door frame, window frame, or gate post).
2. The Magnet Unit: This part contains a small, permanent magnet. This unit is mounted on the moving part of the opening (e.g., the door itself, the window sash, or the gate panel).

The Operational Principle:

• Closed Position (Circuit Complete): When the door/window/gate is closed, the magnet unit is in very close proximity to the sensor unit. The magnetic field from the permanent magnet pulls the two tiny reeds inside the glass capsule together, causing them to make electrical contact. This completes an electrical circuit, indicating that the opening is secured.
  • Many common contacts are “Normally Open” (NO), meaning the circuit is open when the magnet is away and closes when the magnet is near.
  • Some are “Normally Closed” (NC), meaning the circuit is closed when the magnet is near and opens when the magnet is away. This is very common in security systems, as an “open” circuit triggers an alarm.
• Opened Position (Circuit Broken/Changed): When the door/window/gate is opened, the magnet moves away from the reed switch. As the magnetic field weakens, the reeds spring back to their original position, breaking the electrical contact. This change in the circuit (from closed to open, or open to closed, depending on the type) signals the connected system (e.g., a car alarm, home security system, or gate control panel) that the opening has occurred.

Common Applications:

• Security Systems (Homes, Businesses, Vehicles): This is the most prevalent use. Magnetic contacts are placed on:
  • Doors and Windows: To detect unauthorized entry. When a door or window is opened, it triggers the alarm.
  • Garage Doors/Overhead Doors: Larger, more robust magnetic contacts are used for garage doors.
  • Gates: Used on pedestrian gates or even main driveway gates (sometimes in conjunction with the gate opener’s own limit switches) to monitor their open/closed status for security purposes.
  • Safes and Vaults: To detect if they have been opened.
  • Vehicle Doors/Trunks/Hoods: While vehicles have internal sensors, magnetic contacts can be added for enhanced security on specific compartments or custom modifications.
• Access Control Systems: To monitor entry and exit points, log access events, or control other devices based on door status.
• Automation Systems: To trigger actions based on the status of a movable part. Examples include:
  • Turning lights on/off when a door opens.
  • Indicating when a cabinet door is ajar.
  • Position sensing in industrial machinery.
• Appliance Safety: Some appliances use magnetic contacts to ensure a lid is closed or a guard is in place before operation.

Types:

• Surface Mount: Most common, easily screwed or adhered to the surface of the frame and door.
• Recessed/Flush Mount: Designed to be drilled into the frame and door for a more discreet, hidden installation.
• Heavy Duty/Overhead Door Contacts: Larger and more rugged, built for the heavier use and larger gaps often found with garage or industrial doors.
• Wired vs. Wireless:
  • Wired: Physically connected to the alarm panel via wires, offering high reliability.
  • Wireless: Contain a small battery and a radio transmitter to send signals wirelessly to the alarm panel, offering easier installation.

In Vancouver, BC, magnetic contact switches are a common product found at security system suppliers, electrical wholesalers, and businesses that install residential and commercial security systems, including companies like Royal Gates if they offer security integrations for their gate systems.