2) You do NOT need to be an amateur radio operator to do this.

3) You NEED & REQUIRE WRITTEN AUTHORIZATION FROM the FCC LICENSEE that you are authorized to program and use a radio on their system.

IF YOU CAN NOT GET STEP #3. STOP! Your agency could take action legally and personally that you may not desire. GET PERMISSION TO DO THIS!

What you need to determine is the

a) Frequency(s)
b) PL/CTCSS and/or DPL/DCS codes
c) Repeater setup on VHF, which is input and output, for UHF they follow set patterns

Once you have the above, AND WRITTEN PERMISSION! You can purchase a unit like:

http://tinyurl.com/y8cb39u

This will handle BOTH VHF & UHF bands from 136-174 and 400-470. If you need above 470 there are some units that will go to 480.

If you need something in the 30-50MHz range you will need to look else where as these will not work.

If you need trunking of any sort your going to have go thru your agency to do this.

Analog conventional in V/UHF is not a problem.
References :
Designer and builder of public safety radio systems

Odds are that they use the VHF-Lo, VHF-Hi or one of the UHF business/public service bands. Most users still use fixed-frequency FM radios that work on one of a couple frequencies they have access too. If the municipality has some money to throw around and limited frequencies they might invest in trunking radios. This allows x number of municipal services to share less than x number of frequencies but it appears to each that they have their own frequency (assuming the services aren’t all trying to use the frequencies at the same time). These could be analog or digital.

If you just want to listen, that’s easy. A scanner will allow you to hear what’s going on with the squad. Some scanners are portable. They look alot like hand held radios. Make sure it work for the band you need. If the squad uses trunked frequencies, you’ll need a trunking scanner. If your squad uses encryption, you’re out of luck using a scanner.

If you want a two-way hand-held radio, you’ll have to know the frequencies (and thus the band) they work on, if they use trunking, encryption, CTCSS or DCS tones used for in transmitting and/or receiving, tight radio toerance requirements, any special features needed and licensing requirements for your squad.

Most likely, the radio you’ll need is a garden variety 4 channel VHF or UHF FM radio. The place where you buy it from can program the frequencies and tones the squad uses into it for a fee. These radio cost around $200.00 to $250.00 (maybe less). Trunking, real tight tolerances, special features or encryption will be costly and may require you to buy only certain radios.

After all of this, you might wish they USE CBs!
References :

A scanner will allow you to listen to the emergency services but not talk.

A third option if you’re looking at providing services for your community would be to get an amateur radio license (Also known as Ham Radio). After hurricane Katrina the -vast- majority of communications out of New Orleans was through Ham operators that trained privately in emergency communications and handling communications during disasters. An EMT with a ham license could be an invaluable asset during a massive disaster that affects a city’s normal police/fire communications.

As a bonus -depending- on the type of system in use in your area it may even be possible to legally modify your ham radio to talk on the police/fire frequencies (don’t get too excited, you have to be a ham operator, and a member of a club that actively participates in disaster drills to do this legally. Doing so without these conditions could be a violation of federal law and land you in really nasty trouble)

Don’t let either of the last two scare you, I’ve helped people get their ham license with as little as four hours of study time before, and if you do it the correct legal way, you can legally provide a valuable service to your community.
References :
Ham radio operator since I was 12

Trunking radios constantly renegotiate the frequencies utilized for the conversation. This allows for more efficient utilization of limited frequencies because each conversation does not require a dedicated channel. However, it also makes it very difficult to scan trunked conversations because you do not usually know what frequency the next portion of the conversation will appear on.

Trunked radio systems are utilize one or more "Control" or "Data" channels. The data passed via the control channel instructs each radio in the system which frequency to switch to in order to remain on the selected channel. Several utilities are available to monitor and decode some of the common trunking protocols:
References :
Pro AV Guy!