Seek device to close switch when phone line in use

IANAL but you don't need to. Just put a LARGE notice on the phone:

"By using this telephone you agree that your conversation will be recorded by the owner of this equipment. Your permission and that of the other party in your call will be sought before the recording is made available to third parties. If you do not agree, you are committing a theft of service if you use this telephone."

This needs to be duplicated in Braille on the grip of the handset and also in foreign languages if there is a reasonable expectation that Non-English speakers are likely to use that phone.

You forgot the audio announcement for those who can't read! :-)

Various devices could be fitted inside the standard GPO 700 series telephones; one of these was a microswitch which provided an extra pair of hookswitch contacts. I'd been wondering what this was for; could it have been used with recording equipment? I've got a pair of 706 'phones that I've recently set up as a private intercom, and one is fitted with this device; the n/o contacts are connected to the extra wires on a six-wire line cord. Another possible use I can think of would have been to shut down some noisy equipment when you picked up the telephone, but you wouldn't have been allowed to connect your own equipment to the telephone, so I don't know.

That would be analog phone but with a digital interface at the 'exchange' (company office) for dial-up 56k use. Checking loop current with a sensitive relay would do it.

Graham

LMAO!!

On Fri 20Feb 21:24, Dave Platt wrote

Maybe the easy way to do it is buy a premade adaptor like this one for under £2.

How do you wire an optoisolator to go in place of the LED? Presumably the "output" would handle very little current.

Is this optocoupler the same thing?