DCC Specialties Optical Sensor
The Cross Hare Optic Sensors provide a convenient method of "On/Off" switch detection for the Cross Hare. If you have a double track railroad crossing, you'll want to add four optic sensors for the 2nd track. Sold individually.
 
MSRP $1.95  dspoptic
https://tonystrains.com/product/dcc-specialties-optical-sensor