Nihil,

Is this the technique that was used by the 'TV detector Vans' in the UK?

(For those from non-UK shores, all TV-receiving equipment in the UK is supposed to be licenced. At one time, vans drove round outside non-licenced properties and tried to detect a TV being used in the house. Rumour has it they could see what you were watching. They don't bother any more, it's now just a computerised list of TV-owners, probably not unlike a subset of Melissa).