Hush-a-Phone Transmitter Attachment for Antique Candlestick or Wall Telephone.
Silences your voice from nearby eavesdroppers while you scream into the transmitter so that the person on the other end can hear you.
Patent is well marked: PAT. 12-6-21
Complete cast aluminum body with transmitter retaining clips and screw in good condition. Includes sound absorbing inserts and slide on end covers. See photos. What an excellent find!