Abstract: An oil filter restriction sensor device for warning the operator of an internal combustion engine when the engine oil filter has become restricted and requires replacement comprising a sensor body and a threaded adapter for mounting the sensor body between the engine mounting bracket and an oil filter having a filter element. The sensor body has passageways which allow a normal flow pattern for the oil input and filtered oil output through the filter element. A spring biased slidable piston is mounted within the sensor body with incoming oil and filtered output oil pressure applied to opposite ends of the piston. When the oil filter differential pressure exceeds a predetermined amount the piston moves to a position grounding an electrical connector causing an alarm signal to be initiated warning the operator of the restricted filter condition.