@hikari it is, sort of, a hoax. they can't somehow wirelessly detect you being tuned in - that's impossible - but for a while they did have a few vans detecting the brightness pattern changes from people's living rooms when live sports events were on, which could be used as proof of watching TV without a license.

wasn't widespread at all though, and was mostly just done to create the illusion that they could tell and prosecute you for it, to scare people into paying for a license.

@gsuberland @hikari somehow I don't think that's the explanation Hikari's going for :p