From The RadioReference Wiki
Signal Stalker I and Signal Stalker II
The Signal Stalker feature provides a powerful new tool for you to rapidly detect and monitor frequencies for nearby radio transmissions similar to the Close Call feature on the Uniden scanners. Signal Stalker is similar to portable frequency counters but provide many advantages over typical frequency counters.
Signal Stalker feature is more sensitive than portable frequency counters and will detect transmissions at a greater distance. You can also activate the Attenuator to reduce the sensitivity if desired.
Signal Stalker I
You can set Signal Stalker I to work “in the background” while you are scanning other frequencies; turn off normal scanning while Signal Stalker works; or turn off Signal Stalker and use the scanner normally. You can set the (1) frequency band where you want the scanner to look for transmissions and turn on the pager screening feature so the scanner ignores common pager frequencies. You can also set the scanner so it alerts you when Signal Stalker I finds a frequency.
Signal Stalker II
Signal Stalker II allows you to watch for activity on all band frequencies or Police/Fire frequencies only. You can also turn on/off frequency sub-bands using the corresponding number keys.
Signal Stalker II will not work in the background like Signal Stalker I or Close Call.
Once an active frequency is found, the transmission is played through your scanner’s speaker, and you can quickly store it in any of your scanner’s memory locations.
Signal Stalker II functions by rapidly sweeping through the RF spectrum in 1 MHz segments. If RF signal energy is detected in a 1 MHz segment, Signal Stalker II will sweep through the 1 MHz segment in finer steps until the source of the RF signal energy is found.
You can change the normal Signal Stalker II operation to the Special Signal Stalker II operation. If you lock out 5 frequencies within a 1 MHz segment, the scanner will skip that segment in subsequent sweeps.