Mm a valid radio ID which would be assigned by the austin fire or the system admin or the radio shop?
Just curious but if hes only intending to listen in then I thought an RID would be needed if he has TX unless regardless it still TX a transponder signal to the communications center when turned on if its hooked up to the system?
"valid ID" usually refers to the individual ID of a trunking radio, which is set by the system manager to identify each subscriber radio on the system. It requires the CPS, and either a legacy system key or advanced system key for that trunking system to change/modify/program that system into a Motorola trunking subscriber radio. No "ID" is required to monitor a CONVENTIONAL system and the radio can be set to RX ONLY for that channel.
Motorola trunking radios, especially Smartzone and Astro 25 systems, require affiliation to function and there is no way around it on Astro 25 to "just listen". Even legitimately authorized radios in on receive can cause issues during mass incidents, as affiliation occurs and when users cross zone boundaries, channel resources can be depleted by users listening to talkgroups across zones. This happened in the bridge collapse in Minnesota where users on the system far away tuned into the talkgroups in Minneapolis to hear the traffic. This strained the sites in their area and caused system busies for users on other TG's.
This is one of many reasons why you'll be hard pressed to find any system managers who will cut you on a mission critical network "just to listen".
So as others have said, if it's a trunking system, buy a good scanner and antenna. OTOH, conventional professional radios can and do have superior front end, interference rejection, intermod rejection, and usually superior RX audio. Problem is finding someone to program it the way you want it, and with some rare EXPENSIVE exceptions (eg. XTS5000 with FPP, JT1000, etc) you cannot change what is programmed without investing in costly software, cables, and the skill to use it all. Scanners are so much more flexible, and keep in mind, they cover all the RF bands- commercial radios cover only 1 (unless you want to blow 7 grand on a Thales Liberty or Motorola APX7000, or Harris Talk as One).