SPDT changeover reed switch products are a single (Form C) reed switch which is essentially a single pole double throw SPDT reed switch. It is hermetically sealed with 3 leads: a common lead, a normally open lead, and a normally closed reed switch lead. When operated the common contact will swing from the normally closed contact to the normally open contact. This is caused by the magnetic field produced by a coil or the magnetic field from a magnet. When the magnetic field is removed the changeover reed switches common contact will revert back and come to rest on the normally closed contact. Check out our Magnet Interaction page to see animated examples of how reed switches are used in a sensing environment.