Noncontact safety interlock switches are machine safety products that provide a compact, non-contact way to interlock doors, guards, gates and covers. They are made of plastic or chemically-resistant steel and are designed to restrict or prevent access to a variety of hazards. Non-contact safety interlock switches use several types of contacts. Positive-break contacts are normally closed (NC) electrical contacts which, upon actuation, are forced open by a non-resilient, mechanical drive mechanism. In the event of a mechanical failure such as the breakage of a spring or weld, the contact point remains in an activated position. True spring-actuated safety interlock switches are not considered to be positive-break devices. Noncontact safety interlock switches with normally open (NO) contact pairs and pairs of changeover contacts are also available. Typically, changeover contacts are used in single-pole double-throw (SPDT) devices.