when wiring multi family condo buildings in md and washinton dc each condo has those hard wired single station smoke detectors (or combo smoke/co's)in them. they do not interconnect with their neighbor's system but are inter connected in that particular condo with 14-3(if you burn dinner you don't want to evacuate the whole building.) they are 120 volt and are powered by that homeowners panelboard. then we have a fire alarm system that is wired to the sprinkler system water flow switches, elevator lobby smoke detectors and pull stations, when any of these go off it will sound an alarm throughout the building--in each condo and in the main corridors, stairwells,etc. in high rise buildings they will only alarm the floor of alarm and the floor above and below the alarm.
