A safety interlock is a device used to help prevent a machine from harming its operator or damaging itself by stopping the machine if it is used unsafely. For example, microwave ovens are equipped with interlock switches which prevent operation if the door is opened. Household washing machines will interrupt the spin cycle when the lid is open. In industrial settings safety interlocks protect employees from harm by presses, cutting tools, etc, often requiring the operator to simultaneous operate a pair of switches with both hands located well-away from the work area. In many cases, safety interlocks are just such strategically-placed switches.
Sometimes a safety interlock system will be temporarily disabled for a legitimate purpose, such as servicing a machine. This can be done by mechanically or electrically bypassing the interlock, for example, by connecting a wire across a switch, or by taping the switch into position so it remains effectively closed. Unauthorized disabling of safety interlock systems is sometimes attempted by users who want to make the protected device easier to use, or if the safety interlock itself has failed, allowing operation of the machine. Obviously, this can be very dangerous.