The signals change whenever a train passes through the tunnel.
The signals rely on system of relays that are energized by an Arduino microprocessor under the layout. The train trips an ultrasonic sensor hidden in the tunnel to change the signals.
The signal on the right is a former Conrail Trilight made by Safetran and the one on the left is a CLS-20R “Vader” signal also made by Safetran. The signals were purchased from a third party who was able to purchase these from a scrap company.