This is the pressure plate accessory track contactor that Lionel put out to be activated by the wheels of the passing train. The weight of the train presses down on the plate, which activates the accessory, turning it on and then off after the train is finished passing over it.
The 145C was originally intended to operate the 145 Automatic Gateman, but it was used to operate other accessories as well. It can be adapted to activate accessories such as the 151 sempahore, 152 crossing gate, and 45N gateman. It replaced the prewar number 41 which operated similarly.
CONDITION: As you can see, this one is nice and complete. It is clean and working. A few spots of usual playwear. This is a vintage, used item.