Bring signal operation and train detection to your DC or DCC layout. Unit uses photocells to detect engines or cars, so no modifications to equipment are needed. Unit will drive three aspect (red, yellow, green) LED signal heads or position lights (as used by PRR, N&W, NS and Amtrak) and can be used for Approach Lighting or Automatic Block (ABS) signaling. Provides detection for up to four blocks; additional units can be daisy-chained to extend block detection. Can also be wired for occupancy detection in up to four single tracks. On-board LEDs mirror each signal aspect in each of the four blocks for easy calibration without the need to see each signal. Great for large layouts where signals may be hidden by scenery.