I believe you are talking about Priority ID Scan.
To set your scanner for this feature, you'll need to turn on Priority ID Scan for the system. In FreeScan, it is a checkbox in the Trunked System Setup window.
Seconly you'll need to get into the talkgroups section. For each talkgroup you want to be priority, check thePribox in the row containing the talkgroup.
Priority scanning in a P25 trunking system such as ARMER is very different than priority scanning with a conventional system. With a conventional system, the scanner will pre-empt a transmission on a non-priority frequency to check for activity on a priority frequency. That is not the case with P25 trunking. Activity on a priority talkgroup is checked only when the scanner is monitoring the control channel or during a channel delay time (after the transmission ends but before resumption of scanning).
Thus if you are listening to a conversation on MPD2 the scanner will remain on MPD2 until the MPD2 transmission ends, even though MPD1 is "talking up a storm".
One other thing - you could be holding (as in not scanning) on a talkgroup such as MPD3 and there are no active MPD2 transmissions. If there is a transmission on MPD1, then the scanner will go to MPD1 (or any other talkgroups marked as priority).
Yes it is a little disconcerting in that it isn't a "true" priority scanning situation - disrupting an on-going non-priority transmission to see if someone is talkging on a priority talkgroup. (No scanner will do that on a P25 trunk system).
Another little twist may come in play with your specific system. If you have several sites programmed (Minneapolis NS, City Center and Hennepin East), it may only check for MPD1 traffic when the scanner is monitoring the Minneapolis NS site.
