I had the tenant before me install fake fire detectors once. Always a green flash every few seconds but that was the only electronics in there. I only noticed because after a few years, I never had to change the batteries, so I decided to check them.

When you move into a new place, always check they are real and work.

Also, shake the ABC fire extinguishers. The powder can clump in the bottom of the cylinder. Or replace them if they're 15+ years old - the local fire station will take them to use in their training classes.

New anxiety source: not that I will move into such a situation as yours, but that I do so and not remember to check.