21 FIRE PROTECTION EQUIPMENT-NAMELY, FIRE SENSING AND DETECTING DEVICES RESPONSIVE TO PRODUCTS OF COMBUSTION; [ FIRE CONTROL SYSTEMS COMPRISING ANNUNCIATOR PANELS, ] DETECTOR SWITCHES AND RELAYS FOR ACTUATING AN ALARM; ELECTROMECHANICAL DOOR HOLDER RELEASES AND/OR DOOR CLOSERS AND LATCHES [ ; AND AUDIBLE AND SILENT ALARMS AND INDICATORS INCLUDING BELLS, BUZZERS, HORNS, LIGHTS AND SIRENS ]