[CambridgeWorks]

Ah, Selcall! Pye transport scheme used the 2 tone sequential Pyecall, ie 2 audio tones, sequentially sent to call a mobile. Third tone was for group call afaik.
Being a field engineer, based from home, when on call, the van was outside and needed constant monitoring to see if I was called.
Then having got hold of a lowband am PG1AM 2 tone pager, I embarked on mods to my mobile transceiver to enable the pager to "listen" to my mobile tx frequency. Thus, when I was selcalled as a mobile, my modification enabled a tx transpond with my unique 2 tone code and my pager responded to this same code. Brilliant, I could watch tv indoors and be assured I would never miss a call.
Unfortunately, a wiring problem put a low ohm resistor acros the tx keying voltage. Result upon my first transpond was a lot of smoke and burning smell of a resistor.
I had instead invented "Smellcall"!!!
A few minutes with a soldering iron rectified the problem and it was a success from then on. Used almost until the end of my employment, when mobile phones took over.
Rob