Contact Sensor

Contact sensors — also known as door/window sensors, entry sensors, or magnetic reed sensors — are among the most common components in smart homes and security systems. They’re small, affordable, easy to install, and extremely useful for monitoring the state of doors, windows, cabinets, or anything that opens and closes.

How It Works

Internally, most contact sensors use a reed switch, a simple electrical switch activated by a magnetic field. When the magnet is close enough, the reeds inside the glass enclosure touch and complete a circuit.

Some advanced sensors may also use Hall effect sensors (more accurate, but costlier and more complex).

Installation Tips

• Mount sensor and magnet no more than 0.5 inches apart.
• Avoid metal surfaces or magnets nearby that could interfere.
• Use 3M adhesive or screws — most kits include both.
• Test positioning before final placement to ensure reliability.

Uses & Ideas

• Use on drawers, mailboxes, garage doors, or even washing machines (to detect cycles).
• Combine with motion sensors for smart presence detection.
• Use multiple contact sensors to track multi-point entries (e.g., double doors).