Dual Watch lets you program the radio to monitor 2 specific channels.  It will constantly monitor these channels for activity.

Tune to the 1st channel you want to program. Press and hold the DW button until "DW" begins flashing on the display. Immediately tune to the 2nd channel you want to program.  (You have 4 seconds to start changing to the 2nd channel). Immediately press and hold the DW button until the "DW" icon stops flashing. (After changing to the 2nd channel, you have 4 seconds to press the DW button). The radio should now be scanning the 2 channels. If not, try turning up the squelch.