Smoke detector won't twist off

[Kay March]

Out of five smoke detectors in one of my rentals, one won't twist off to allow replacement of the battery. I had no trouble with the other four smoke detectors, but this one seems to be fused in place. I can't twist off the cover or even the entire smoke detector at its base. It hasn't been painted, and there's no apparent damage. Please tell me I don't have to hire an electrician to do what should be an ultra-simple little chore!