Comment by foundart
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...
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.
It is still way more difficult to localize a local oscillator (especially one that's trying even slightly to shield itself) than something trying to transmit to a tower a few miles away.