The ability to track down a receiver is a technique I call scanning for scanners. The local oscillator in your receiver can radiate a signal. In some cases it can be detected at quite a distance.
I have used the following technique to actually determine what room the scanner was in.
I will use the example of a scanner that is scanning 155.475 MHz. Every time the scanner is tuned to that frequency the LO will be operating at 144.775 MHz (assuming a 10.7 MHz IF and low side injection). If I tune another scanner to 144.775 MHz there is a good chance any scanners scanning 155.475 MHz in my neighborhood will be picked up.
An interesting side to this is the LO can be modulated and all sorts of interesting pranks come to mind. I did this with a Bearcat 250. The proper location for tapping into was found with another technique of using my finger to locate a point where a hum could be heard on a secondary receiver.
The Bearcat scanners liked to use a non standard 10.8 MHz IF.
I think the furthest range I have ever seen with a scanner (Bearcat 210 to be exact) was about 1/2 mile. That was fun using a yagi antenna and walking past the house that was causing our problem. The home owners were standing in the front room looking out their window as we made our first pass. The yagi kept pointing in their direction. I wonder what thoughts they were thinking as we DF'd their scanner.
I have used this to build listening profiles on nearby scanner listeners. Some areas you will be able to hear more than one scanner.
One time I began to hear a whole set of these pulsed signals on quite a few fequencies around 147 MHz. After noting several of the frequencies I was able to determine the scanner I was hearing was tuned to cellular frequencies. I built my list after calculating the proper frequencies to tune to and then looking at each of these frequencies. I walked the neighborhood with my handheld and found the house. Oddly enough with my antennas on the house I was visited one day by the brother of the scanner owner. After I showed him my schack I asked what house he lived in and if they had a scanner in the house. I am not sure what he was thinking either when he left my place.
If you own more than one scanner you might have already stumbled on this. If
you haven't then you can start to do some of your own detective work.