Sound operates by sensors locating movement of passing train. The optimum operating distance of the unit is about 2.5"/60 mm from the nearest point of the track. However, due to aspects outside of our control, such as brightness of general layout area, operational speed of train, or even gloss or matt paint finish of the train, the operating distance could vary from between 2"/ 50mm up to 7"/ 100mm.
If the power to the unit is subjected to a sudden and unexpected surge or drop in power, then the "trip-switch" within the unit will operate as a safeguard. If this should happen then please disconnect the power (wires) and leave the unit for 60 seconds to re-set itself.