(Anyone else here who is an emergency responder, jump in)

Be careful when you use a scanner to get information about emergencies. Not because of the legalities of it (check local laws, especially for mobile use) but because over the air (OTA) communications are increasingly a small part of the overall information flow, and OTA communications are still highly fragmented in most jurisdictions - EMS and Fire and Police and Roads Department and everyone else operate on different bands, with different radios and so on. At the dispatch center, they have an array of communications gear that lets them hear and speak with multiple agencies, unless you're ready to drop a lot of money on a lot of scanning gear, you'll never actually get the big picture.

Then there is the matter of how what seems important on the scanner is masking what's important to people not in the area of the emergency.

If you were listening to a scanner when the bomb scare happened in NYC a few weeks ago, you would not have heard a thing of importance about anything other than the immediate closure zone - and there was much other stuff going on that day, in particular incredible traffic at the tunnels.

Just remember that scanners are handy - but not at all the "big picture" information that you need.