Capture the action of modern railroading with this accessory that includes a fully-assembled PC board with reed switch and two incandescent lamps. Lamps come on at about 3V and remain on until the unit senses a hidden magnet, which causes them to alternately flash on and off until the unit senses a second magnet, which returns them to constant on. Includes eight bi-polar magnets, enough for four crossings, additional magnets are available separately.