Eavesdropper phone on German ebay

[Willytx]

From the front it looks like an ordinary European Ericsson phone. Around back is a second receiver for someone else to listen in. Hostage negotiations perhaps?

http://tinyurl.com/6dnlv5p
( dead link - 10-10-21 )

ebay.de item number 190512227244

[gpo706]

In the UK they were called "watch receivers", and seems most French ones came as standard, well SOCOTEL 63 series seem to.

They are also referred to as "Mother-in-law receivers".

[GG]

These were common on that generation of French phone (which does not have a ringer in the telephone: they used central ringers), and almost universal on the S-63 which looks roughly like a GPO 706 (and has a ringer with bells that sound very much like a WE 500). 

These were intended for family conversations, secretaries taking notes, and anyone who wanted "stereo" (binaural) reception by holding it to their other ear. 

The German version of that, found occasionally but not often on German type 611 phones, is cleverly designed to be very light and to hang on one's ear thus leaving one's hand free.  I'm almost certain I have one that's equipped that way, but I can't recall where it went at the moment. 

The English version is rare, and the US version is as rare or more so. 

[Owain]

They were also used for hearing impaired people so another person could sign or lipspeak the distant party.

[Willytx]

I guess way back when, it was cheaper than putting in an extension. It still would come in handy for the police to listen in during ransom calls!