1996 Century seatbelt retractors

While working on my '96 Century's electric door lock system, I noticed that both the upper and lower seatbelt retractors on the door had a cylindrical object that was quite HOT to the touch. These parts were about 5/8" in diameter, and looked a little bit like an old distributor condenser. There were two small wires connecting to each of these objects.

My questions are:
1. What are these items
2. Do they draw power from the battery all the time, or just when the door is open?

The seatbelts seem to be working ok, so I don't think there's a problem, but I'd sure like to know what these thingies are!