Marklin 7555 - Reed Contact Switch
For use at a suitable point in K Tracks or in C Tracks. The switch contact (reed contact) triggers a pulse when a locomotive or car with floormounted switch magnet passes by. Switching current to 2 A. Because the switch is mounted off center on the track, it will only get activated in one direction.
Use magnets 7556, 7557 and 7558.