In the mid-1990s, our family got a cheap (I assume, since we weren't rich) but at least brand new telephone which either had two wireless "units", or one (my memory is a bit foggy on this detail), but the point is that, you could take the unit(s) with you outdoors, for example sitting in the garden, even going as far as into a nearby store (150 meters away), and it would still work to talk into, somehow communicating with the base unit in our house.
It also allowed you to press a "local call" button which would skip the telephone network and just ring the other unit (or the base unit; I'm unclear on this) directly, then working as two-way walkie-talkie. This was extremely cool to avoid having to shout that dinner is ready all the time. Mum would just press the "local call" button on the base unit next to the kitchen, and we'd get a signal. (Really, we didn't even need to pick up the phone -- the signal itself was enough to know that we were supposed to come in or come upstairs.)
I find this concept very fascinating, but I'm confused about how it technically worked:
- How was it able to work so far away from the house? What if others also had the same model/make phone? Would we not get each others' signals then?
- Was this encrypted in any way, or was it just blasting out all of our "private" conversations all over the place whenever we were talking into its units? I don't remember it coming with any warning note saying something like: "Please note that anyone can listen to your conversations with a radio receiver!"
- Was the "local call" feature different in any way from the normal wireless mode between the unit(s) and the base unit (which of course was connected to the telephone network by wire)?
I cannot remember which brand or model, unfortunately, but I suspect it's as it usually is: it was not some unique invention but rather one of countless clones of some original invention that numerous companies created with "cookie cutter" blueprints.