D

ACOUSTICONS, CHURCH ACOUSTICONS, ACOUSTICON BATTERIES;INTERIOR COMMUNICATING TELEPHONE SYSTEMS FOR OFFICES, BANKS, FACTORIES, ETC.; INTERIOR TELEPHONE SYSTEMS FOR APARTMENT BUILDINGS PROVIDING COMMUNICATION BETWEEN VESTIBULE, APARTMENTS, JANITOR, TRADESMEN, OR OTHER ESSENTIAL POINTS; LOUD-SPEAKING PAGING OR ANNOUNCING SYSTEMS FOR LOCATING DOCTORS IN A HOSPITAL, ANNOUNCING SYSTEMS EMPLOYING LOUD SPEAKERS OPERATED FROM CENTRAL TRANSMITTING STATION, LOUD-SPEAKING LIMOUSINE TELEPHONES,RADIO LOUD SPEAKERS, RADIO RECEIVING SETS, SWITCHES FOR RADIO RECEIVING SETS WITH ONE OR MORE LOUD SPEAKERS, RADIO LOUDSPEAKING RECEIVER UNITS FOR ATTACHMENT TO SOUNDING BOARDS OF PIANOS; LISTENING DEVICES EMPLOYING SUPERSENSITIVE TRANSMITTERS AND HEADSET RECEIVERS FOR USE BY DETECTIVE AGENCIES, POLICE DEPARTMENTS, ETC.; AND SENSITIVE TRANSMITTERS USED AS ESSENTIAL PARTS OF BURGLAR ALARMS AND VAULT PROTECTION SYSTEMS WHOSE OPERATION IS CONTROLLED BY SOUND WAVES