How are hotel-style door handle/keypads powered?

I live in on a college campus in an apartment where to get in you must first insert a smart card then punch in a pin and the door will unlock. The unlocking mechanism is not very audible and there are LEDs on the lock. I mention these things because the device I assume draws very little power. I cannot find a power source through the door hinge, or anywhere else. It must be battery powered right?

I share this apartment with 3 other students who all probably come and go at least a dozen times a day. With all that power being drawn to “unlock” the door in a secure fashion, how is this thing being powered? Do they maintain them with new batteries? Are they powered by the action of opening the door and turning the handle? Ideas?