In summary, a reed switch is a small electromechanical device having two ferromagnetic reeds hermetically sealed in a glass envelope. When brought into a magnetic field, the reeds will close, creating a switching function. When a reed switch is packaged into a different form or housing, it is then referred to as a reed sensor. A permanent magnet can be used to actuate the reed sensor contacts. In yet another form, a reed relay has one or multiple reed switches inside an electromagnetic coil. The reed switch contacts remain in their normally open state until the reed relay coil is energized, producing a magnetic field strong enough to close the reed contacts. Since these devices are hermetically sealed, they can exist or be used in almost any environment. Being protected from the outside environment, the contacts are not susceptible to wear and will typically perform billions of reliable operations.