21 SECURITY AND FIRE ALARM EQUIPMENT-NAMELY, HOLDUP ALARMS, ALARM AND CONTROL LOCKS, PHOTOELECTRIC SENSORS, ULTRASONIC SENSORS, MERCURY CONTACTS, MAGNETIC CONATCTS AND SWITCHES, ELECTRICALLY CONDUCTIVE WINDOW AND DOOR SCREENS, FRANGIBLE AND ELECTRICALLY CONDUCTIVE MONITORING STRIPS FOR WINDOWS AND DOORS, ALARM SIGNAL TRANSMITTERS, ALARM SIGNAL RECEIVERS AND RECEIVING STATIONS, AUDIBLE BURGLAR ALARMS, CORDS AND CONNECTORS