"Due to inertia some machines may continue to run after their power is removed. This can create a situation where it is possible to access the hazardous areas of the machine when they are still in a dangerous state. The solution to this problem is to lock the hard guarding access door closed until the machine is given enough time to wind down. The SLK and SLM series have a built in solenoid which can lock (or unlock) the activation key into the switch, preventing the door or gate from being opened."