Unless your job is odd, existing devices in the demolition space don't need to remain active, with the possible exception of say an elevator smoke detector or a sprinkler valve that affects occupied spaces. I have never been on a job where we had to have active fire alarm (smoke detectors and horn strobes) in the construction area. Please clarify.
(edit) It makes no sense to keep devices in the construction space active, since they are certainly not going to be reinstalled in the same location. Smoke detectors are not only undesirable, but illegal in a construction zone. One at an elevator lobby must be covered during the day and uncovered only at night when no construction is going on. It is somewhat possible you have a jurisdiction that requires some sort of strobe coverage during construction but that should merely be a device temp wired and mounted anywhere.