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H04M1/00—Substation equipment, e.g. for use by subscribers
H04M1/02—Constructional features of telephone sets
H04M1/19—Arrangements of transmitters, receivers, or complete sets to prevent eavesdropping, to attenuate local noise or to prevent undesired transmission; Mouthpieces or receivers specially adapted therefor
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FR782809D1934-12-181934-12-18Obturateur de micro d'appareil téléphonique, assurant l'inviolabilité des conversations avec des tiers
ExpiredFR782809A
(fr)