This is the HE-7847 magnetic reed switch, normally closed.

Two parts, a switch and a magnet, with no physical contact between them. That makes it the answer for detecting a door, window or panel opening where a plunger has nothing to press against, or where a mechanical switch would be visible or in the way.

Normally closed means the two wires are connected to each other at all times, and the connection breaks when the magnet comes close. Check which type your system expects before ordering, because fitting the wrong one gives you a permanently triggered zone.

Features

• Normally closed
• 12 volt
• White
• Water and weatherproof
• Very small

Need the opposite? See the normally open version. For a switch that survives being driven over, see the HE-7850 heavy duty.