This is a miniature normally open contact type reed switch. When the switch is exposed in a magnetic field, the two ferrous pins inside the switch pull together and the switch closes. After removing the magnetic field, the leads separate, and the switch opens. This makes for a great non-contact switch and carries up to 1.2A.
The switch has low contact resistance and is ideally suitable for signal switching applications, reed relays, security, monitoring, limit sensing, etc. It is a small and easy-to-use module and can operate in a variety of environmental conditions. It operates very reliably in the -50℃ to +140℃ temperature range.