Abstract: A portable, compact, freestanding sensor housing is configured to be stably and removably affixed relative to a metering device having a movable indicator element. The housing includes a transmitter for emitting electro-magnetic radiation and a receiver for receiving electro-magnetic radiation. The transmitter and the receiver are positioned to define a reflective region within which an object will reflect electro-magnetic radiation emitted from the transmitter toward the receiver. A signal generator, in communication with the receiver, generates a signal indicating that the movable indicator element is located within the reflective region. A sensor warning device affixed relative to the metering device will thereby generate a signal when the movable indicator element is located within the reflective region.