The N800 has a built-in FM radio too, that would fit right in in 1978 (and earlier). In 1979 I bought my first battery-only LCD clock radio.. it looks quite like a just slightly larger N800, just without the LCD screen. So it could hide like that for a while..

And Karel said 'going back to 1978'.. that's perfect, because the first experimental GPS satellite was launched in 1978. I don't know if it transmitted anything on the civilian band yet though. But in the early eighties more satellites were launched, and where I worked at the time there would regularly arrive engineers with huge racks of equipment to test the GPS system, this was long before it became operational. If they did transmit anything on the civilian band back then then I imagine those engineers would be quite shocked to see my BT GPS used with my N800!