In the old days it was probably possible to actually detect a TV based on the intermediate frequency. There's no transmitter but neither are they TEMPEST-rated

In the old days it was probably possible to actually detect a TV based on the intermediate frequency. There's no transmitter but neither are they TEMPEST-rated equipment, there would be leaks. But that only detects that there's an operating receiver, not what it is receiving. Originally, live was the only option--but not any more.