A displacement sensor that includes a stationary printed circuit board which includes a first capacitor pad, an indicator, and a battery electrically communicating with the first capacitor pad and the indicator and a sliding card which includes a second capacitor pad, the first capacitor pad and the second capacitor pad being orientated to face each other and in an overlapping relation to each other. An overlap being defined by the first capacitor pad and the second capacitor pad, wherein the overlap of the first capacitor pad and the second capacitor pad generates a capacitance, the generated capacitance changes as the sliding card moves as a result of a change in the overlap of the first capacitor pad and the second capacitor pad. The indicator is activated when the generated capacitance change reaches a threshold value.