While a transmitter is indeed to a first approximation a beacon screaming 'I'm here!', do keep in mind that these antennas are highly directional, and while the

While a transmitter is indeed to a first approximation a beacon screaming 'I'm here!', do keep in mind that these antennas are highly directional, and while there will be side lobes, you basically need to be in the beam path to even detect it's there - complicating matters significantly. Besides, the antenna itself is rather small, and can be hidden inside just about any structure transparent to RF in the relevant frequency bands - say, a seemingly innocuous water cistern on the roof, for instance.