Reed Relays

As a relay is a switch controlled by an electromagnet, so a reed relay is one or more reed switches controlled by an electromagnet. The contacts are of magnetic material; thus the electromagnet acts directly on them rather than requiring an armature to move them. Sealed in a long, narrow glass tube, the contacts are protected from corrosion, thus are ordinarily plated with silver rather than precious metals. The most common reed relays of the late 1930s through the 80s had two reed switches inserted into holes in the bobbin. Since the moving parts are small, reed relays are capable of faster switching than most others.

Reed Switches (wiki)
Reed Relay Applications