A removable sensor assembly for non-intrusively sensing instantaneous speed of an engine comprising a crankshaft having a respective end equipped with an externally accessible bolt, the removable sensor assembly comprising: a housing comprising a recess configured to removably receive and engage a portion of the externally accessible bolt; and a force sensing device received in the housing, the force sensing device being configured to wirelessly provide information indicative of angular motion of the crankshaft, the force sensing device comprising: at least one coil; a power supply for providing an excitation to the coil, wherein the coil provides a first signal and a second signal each corresponding to the movement of the housing, the first signal corresponding to the resistance of the coil and the second signal corresponding to the inductance of the coil; and a signal transmitter coupled to the coil to receive and transmit the first signal and the second signal.