The Uniden 996XT or its portable sibling 396XT would be a good scanner. Unfortunately they are no longer in production, having been replaced by the 996P2 and 325P2.
Also programming them for the ARMER system may be a little more challenging. That's because there are certain limitations on the number of groups. This can be overcome with time and patience.
My suggestion is a Home Patrol 1 or 2. There is a minor amount of programming, mostly updating the database in the beginning. After that, you enter your zipcode and can be running. There is some advanced programming (creating Favorites Lists) for this scanner, but only if you want to refine what you are monitoring.