When a smoke detector in an elevator lobby or machine room-and the hoistway, if protected-actuates, it must indicate an alarm condition on the building fire alarm system. Also, the detector must cause a separate and distinct visible annunciation at the control unit and require annunciators to alert fire fighters and other emergency personnel that they may no longer safely use the elevators. This need not actuate the system notification appliances as long as the alarm signal indicates at a constantly attended location. An exception exists in the requirements that permit the detectors in the machine room and elevator hoistway to initiate a supervisory signal rather than an alarm signal.
Interfacing the fire alarm system with the elevator recall system will maintain safety by preventing the occupants from using the elevator and possibly becoming trapped in the hoistway or riding in an elevator car called to the fire floor where they would likely perish when the doors of the cab open. Interfacing the fire alarm system with the elevator recall system also allows the firefighters to use the elevators as safely as possible during their fire fighting efforts.
http://www.nfpa.org/~/media/Files/forms%20and%20premiums/NF72HB07_CHS2.pdf