Some of the techy things I'm involved in mean I monitor some radio frequencies very close to these devices and quite often I'll tune through their radio band as I go from a to b. You're right, they are VERY effective bugging devices as they have a very sensitive microphone in them, because they are all built really cheaply there is no privacy option so it's a bit like having your house bugged and then broadcast on the radio for anyone with another listening device who lives locally. I can hear dozens of them within a couple of miles, don't think they only go as far as your house or neighbours, they can easily go across town And yes, I have even heard THAT happening on them Never leave them switched on for longer than necessary, although for a few more quid you can now buy DECT versions which are digital and can't be listened in on by your neighbours.
Paul
Shopping when the football was on worked a treat, empty roads, half empty shop and no queues!