How much current could I take from the 50V phone line before I get problems
I have got plenty of old phones, some antique, some have buttons on the top .
If I modify two phones with these push button switches on the top and fit inside (or outside ) a piezoelectric sounder with suitable series resistors.
I could use the spare pair to the workshop and wire it up so that it sounds the piezo .
Lift house phone off cradle dial 1 or press cradle switch to get rid of the dial tone, press push button on house phone this will ring the workshop piezo (buzzer) then I should be able to use the two phones as an intercom, it should work the other way around eg workshop buzz house phone.
The two modified phone would still make external calls and receive them (I hope)