See page 73 in your manual for how to set up the Priority Scan feature. That said, priority will only set the scanner to check for something on that frequency/trunkgroup more often. What it can't do is know that a transmission is active on a priority scan channel while you're actively listening to another channel (there's only 1 receiver availble so if it's using that to let you listen to something, it can't use it to check the priority channel(s) for activity).