I think the heated door locks are standard items on the 7-Series (please correct me if I'm wrong).

Just wondering, but how does heated door locks work. Obviously, it keeps the lock cylinder from freezing during winter, but:

Is it constantly on all the time? Isn't that draining the battery?

Is there a temperature sensor that if it reaches below a certain temperature, it heated door locks kick in?

Is it like the heated mirrors in which they heated door locks are only active when the vehicle is on? (kind of silly)

Thanks.