US Patent 7928330 Safety switch

There is provided a safety switch having a housing configured to receive a removable key, and a mechanism arranged to be operated when the key is moved from an engaged position to a partially disengaged position, the mechanism being arranged to cause a signal to pass to a separate apparatus, wherein the safety switch further comprises a lock which is controlled by the separate apparatus and is arranged to prevent the key from being fully disengaged from the safety switch until a signal has been received in response from the separate apparatus.