Safety relays are types of relays which are used to keep a system safe. Safety relays are especially used for emergency shutdowns and other safety-critical applications. They are used to switch off the system quickly in the event of an emergency to prevent any further harm or damage. Safety relays generally feature two- or three-hand control which ensures that it is onl y possible to switch the system off when both or three of the control functions have been correctly operated. They may also feature redundant contacts for increased safety and can detect a number of different types of faults, such as voltage, current or resistive faults. Safety relays also allow for other safety-related features, such as monitoring of the position of a guard door, detection of improperly connected safety devices, etc.