Some kinds of receivers can be localized because they convert input frequencies to a standard internal frequency for more convenient processing. See https://en.

Some kinds of receivers can be localized because they convert input frequencies to a standard internal frequency for more convenient processing. See https://en.wikipedia.org/wiki/Superheterodyne_receiver#Local_oscillator_radiation https://en.wikipedia.org/wiki/Superheterodyne_receiver#Local... It's how the TV detectors work in countries, such as the UK, that charge a license fee for TVs. Military radios can't use this common technique because of the risk of detection. I suspect pagers only receive on 1 or at most a few frequencies. If that's correct, they wouldn't need that technique.