Carl, thank you very much. Is it common for police to have scanners in their homes?
Not so common ... but, they almost all have their police radios if they are assigned, and some may keep them on all the time to scan traffic. I know many officers that do that, but far more keep the darn thing off when they are at home. I turn mine on, but then, I'm responsible for what happens so there are times when I want to know what is going on. When I was just an indian, I almost never turned it on at home.
Can you assign a percentage?
Not really. I'd say close to 3/4 have a scanner or radio of some kind at home, but probably less than 25% might be listening. But, that's just a guess.
Far more likely is someone else was listening and called him ... if he moved the vehicle as a response to the radio call.
And, yes, it is also possible that someone at the agency (dispatch, admin, patrol, etc.) called him and told him to move the truck.
If so, is it legal for an officer to evade law enforcement against himself by monitoring a police scanner; sort of a case of "sworn officer" insider trading.
If the general public can do it, the officer can do it. So, yes, it is lawful for him to do it.
That should be a crime as the scanner would be a TOOL to be used by the officer to avoid citation or arrest.
As nice as that might be, and as useful a tool as that might be for use against dopers and the like, it's just not in the law.
Also, how do scanners alert the operator? Does the screen have to be watched constantly or does it emit an audible tone?
It's audible. When a channel that you are scanning has traffic, it comes over the radio. Depending on the radio or scanner, you can set certain channels to have priority (like the primary dispatch channel for where you live, perhaps). So, if he was listening to his scanner - even in the background - chances are he would key on his address being put out over the air ... I know I would.
When i was in So. Cal. I used to train my officers to pick out pieces of conversations by scanning two primary channels, our car-to-car channel, the primary dispatch channel for a neighboring agency, the AM radio set to news talk, and I would carry on a conversation with him or her. I would then randomly ask where another officer was and what kind of call they were on. In other words, the officers were trained to key on important pieces of conversations through a blizzard of "noise". Any officer on the job for a year or more will develop that skill to one degree or another.
Regards,
- Carl