Abstract: A machine such as a centrifugal pump has a rotating impeller which may get out of alignment if there is bearing wear or if the impeller becomes loose on its supporting axle. A misalignment sensing probe and switch may be installed through the housing of the pump with it probe tip in close proximity to the impeller's face. If the rotating impeller migrates out of alignment it will abrade the tip of the sensing probe. Inside the probe body there is secured a stranded insulated electrical conductor with one of its ends in the tip while the other end extends beyond the other end of the body and is connected into an electrical circuit. Abrasion of the tip will force contact between the stranded electrical conductor wire and the body of the probe. This closing of the switch will activate the electrical circuit which has been designed to shut down the power source and/or activate an alarm and thus avoid destruction of the pump.