The car phone.
My electrical expert friend saw the huge luggable phone I was using for a previous job, it was huge, lasted about a day per charge and was very difficult to carry on my bike.
For a laugh my friend built a car phone, it was large filled his boot, and worked.
At his parents home (edge of Cotswolds) he connected via some electronics to deal with pulsing ect to a transmitter and a receiver, he had another pair
in his boot, then used an old home phone as a hand set. It looked like a joke car phone except it worked when in range of his parents, this covered the
Gloucester and Cheltenham area.
I had a phone call - it was Nick, "Guess where I am calling from?", "The car?", "Yes" - I had found the hand set at home!!!!
This lasted a couple of weeks until he was bored.
Oh well a pulse dialling car phone was fun for a while - at least the calls were cheaper than the 1/2 ton luggable I had to use when on support.