The invention relates to a signal connector, which mainly includes a leading structure provided between the shell and the body. A relay and control switch are installed in conjunction with the existing seat belt switch circuit underneath a patrol car seat such that they are undetectable by an occupant. The source processors and the destination processor are synchronized together. When the acid is further spent, the fluid viscosity declines eventually returning to a low viscosity state, allowing for easy cleanup. The contact portion is operable to establish a conductive path between the dental instrument serving as an electrode and the length measuring circuit portion.