Shoot back in the 60s they could listen in on cradled phones in a room due to the micro voltages created by the transducer
And a few years later, the line powered transmitter.
Trim the antenna for your desired frequency on the am band.
They used to be ~ $2.00 each.
Simply installed in the network interface box outside the house.
When the phone companies started adding that box (first heard about it in FL), future "Florida Man" types would mosey on up to snowbird houses, small phone in hand, plug the network side into the phone, and make 900 number sex calls.
How surprised were the Winter residents getting their sky-high phone charges on their monthly bill from their "Summerized" and unoccupied home.