The reed switches comprise two ferromagnetic reeds placed with a gap in between and hermetically sealed in a glass tube. 

 The glass tube is filled with inert gas to prevent the activation of the contacts. 

 The surfaces of the reed contacts are plated with rhodium or iridium.

 The reed switch is operated by the magnetic field of an energized coil or a permanent magnet 

 which induces north (N) and south (S) poles on the reeds. 

 The reed contacts are closed by this magnetic attractive force. 

 When the magnetic field is removed, the reed elasticity causes the contacts to open the circuit.