A pre-cover-opening power-off method, comprising the steps of: (a) fixing a bolt casing to a bolt; (b) connecting a motion sensor to a safety protecting and monitoring unit in a wired or wireless manner; and (c) activating the motion sensor to send out a command to permit power delivery for an electrical equipment to operate, and when the bolt casing is taken off, the motion sensor is activated to send out a command to cut off a power supply for the electrical equipment or give out an alarm.