Reed switch guide - fochica/fochica-wiki GitHub Wiki

A reed switch is used in combination with a chest buckle to make a chest buckle sensor. This sensor provides an indication about the seat's occupancy based on the state of the buckle.

A reed switch is a mechanical component that closes a circuit when a magnet is near. Usually there are two parts, the switch and the magnet. When the two are next to each other, the switch is closed.

Search for "reed switch". You will find basic reed switch components in tiny glass tubes:

as well as ready to use sets of switch and magnet, typically intended for use in alarms.

If you are making an advanced build and aiming for a compact size then a "barebone" switch might be a good fit for you. Mind that you will need to source your own magnet and that you will need to install the switch in a way that it is protected. Otherwise get a ready-made set in a protective plastic casing.

Note that reed switches are cheap components, so they are often sold at bulk for roughly the price of one piece.

The switch typically comes with short wire. Extend the wire (by soldering or twisting more wire) to reach the length you need from the buckle to the device.

Plan for an orientation that will create least obstruction. If needed route the wire next to the seat buckle upwards or downwards.