Reed relays are electrically-operated switching devices that consist of two thin, magnetic strips (reeds) encapsulated in a glass envelope. When a coil around the glass envelope is energized, the resulting magnetic field brings the reeds together and closes the contacts. Most reed relays have higher coil resistances and provide faster switching speeds than standard relays. With normally open (NO) devices, the relay contact pair is open when the coil is not energized. With normally closed (NC) devices, the relay contact pair is closed when the coil is not energized. Changeover relays typically have one set of Form C contacts.