Some ham radios have gps trackers built in.
Some trucking companies use them
I believe there are devices to put in the cars of your kids to track them driving.
Some people carry them when hiking for emergencies.
People use them as a hobby to find packages hidden like a hue and go seek situation.
There have been stories of the feds pitting them on vehicles of interest.
They are getting smaller and more affordable than they used to be. With bulletproof cases with magnetic attachments, now days all you need is a smartphone. The old ones you had to get their special monitor and the devices were huge with crappy battery life. Most want you to pay their monthly memberships to track them but lately a few have free programs out there.
Great for tailing marks without having to aggressively follow. You still need to physically be there when they stop for pictures to prove who comes and goes but if you have mutable marks and no man power you can follow one and tag the others for later plus picking up new points of interest to add to your dossier. You have all the stopping points and times recorded into the program.
er.... so I've heard.
Legality?
I've only used them in CA where I just assume that everything is illegal.
There's one in your phone, and many other devices you own, maybe even your car/truck, that you didn't ask to be put in there and may or may not have consented to be used for or against you.
IMO, there is way too much "If you're not going to do anything wrong you don't have anything to worry about" attitude by the sheeple. Not that I plan on doing anything wrong, of course. Until wrong is redefined.
I've pulled numerous ones out of cars over the years. Used car lots will wire them in so they can recover them if you don't pay. They frequently don't understand how CAN busses work, and tie them into a system that keeps the car from going to "sleep" properly, and keeps killing the battery.
In Indiana, it's covered under stalking & wire tapping laws as far as I know.
Court order, parents can GPS their own vehicles when kids drive them, but you can't track someone without their knowledge.
On the other hand, we have friends with automotive repair garages, and they have a piles they found on customers cars the customers didn't know about.
Owners haven't show up to get them, so you have to assume illegal.
Even oil change places sometimes offer inspections for trackers... So I have to conclude it's getting much more common...
If someone tracks me, they are going to get pretty bored!
I beat a path to the same few places over & over again...
Or they could just ask, I don't really care if people know where I go since none of it is illegal.
A guy we know out in CA has about 50 of them stuck to the inside of his pickup truck bed...
Owns a security business, and when he finds one he hauls it around until the batteries go dead (and beyond).
Confuses the person(s) tracking his customers...
He's stuck them to stray dogs and long haul trucks before just to screw with whoever is tracking his customers!
Not sure that's legal, but it's funny!