How do reed switches work?
A reed switch is a none contact electronic switch. It opens and closes as a magnet moves in and out of proximity.
They are great for protecting opening zones where a conventional plunger switch would not be practical. Common uses are Ute canopy windows, Ute hard lids, and camper van doors.
The Magnet is generally fitted to the item that moves, the switch in turn is fitted to the vehicle. If the magnetic contact is broken (magnet moves out of range) then the alarm triggers.
Good times to uses a reed switch
The are many other uses for a reed switch. I have fitted them into the glove box on vehicles so it turns on a LED light when the door is opened. As the magnet works through plastic it is totally hidden.
The photos show a reed switch which I installed on a hard Lid of a Toyota Hilux.
Being a builders vehicle I knew there was a danger of the switch getting knocked off. I made up a custom metal bracket to protect if from abuse.
Wireless Reed Switches
Autowatch make a wireless reed switch that works with some of their alarms.
Other types or car alarm sensors?
Reed Switches in more detail
The ElectroninsNotes YouTube channel has a great video that dives deeper into reed switches
