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