A similar suggestion to the other poster:

Try relocating one of the troublesome units to someplace nearby but not mounted to the ceiling. The top of a bedroom dresser, the floor, a bathroom countertop, the top step of the stairs, halfway down the stairs, hanging from a wall (picture hook)… just get creative.

And since you haven’t mentioned it, I presume these are all smoke detectors? Do you have any heat detectors or carbon monoxide detectors installed?

and what looks to be some sort of dried landlord repair fluid.

Not that the landlord needs to be really broken before you’re able to see the benefits of using the repair fluid.

For slightly broken landlords, don’t waste perfectly good repair fluid on them.