Experience with GPS trackers - thieves' reactions? I'm interested in experiences what happens in reality when a bike with a GPS tracker is targeted / stolen by thieves. 

There are GPS trackers with a SIM card that will send an alarm to your mobile when moved, and you can also query the location remotely by sending an SMS text message. Some are specially designed for bicycles and are hidden e.g. in the seatpost, but they are fairly expensive. 

What I'm interested in are the cheaper ones costing around 20-40 UK Pounds. They are too bulky to be hidden inside the frame, so it's a question whether they are noticed by thieves or not. For example, they look like rear lights (but can be screwed to the frame so that it's at least time-consuming/fiddly to get them off).

My question is if there are any experiences how thieves actually react to those. In particular:


Are there examples that thieves have checked the bike for such devices, taken them off and nicked the bike anyway?
Conversely, are there examples that thieves didn't notice them and got caught?
Or perhaps thieves notice the device and then leave the bike, as it's an additional risk? The alarm is sent at the first movement, so if the owner is nearby, the thieve would get only a few minutes.


My bike is always locked with two locks, and it's in the medium price range (about 600 pounds inc dynamo lights, mudguards, rack etc., but a few years old and well-used), so it would be most likely targeted by reasonably equipped thieves to sell on the local second-hand market, but not really experts looking for expensive bike parts.

There is another question asking for experience, but that one is more focussed on the technical practicalities, with good comments about ease of use, need to recharge, mobile phone SIM card charges etc.. I'm aware of all that and it doesn't have to be repeated here. But there are no answers about experience with actual thieves.
I've got a friend who had a cellphone stolen.  She used the provider's tools to locate the phone down to a suburban address, and went to get it back.  The teenager who answered the door knock said there was no such phone there.  Her brother called it and they heard it ringing in the background.  Some more people turned out of the house and denied her entry.  She phoned the police with this info and they weren't interested, plus advised her that entering the house to recover the phone would be illegal and that she should write a written official complaint at the police station.  She went to the police station to do a report. Her phone was turned off/wiped before she could demonstrate the location to the officer taking the report.

The phone was never recovered.

Answer GPS tracking by itself isn't going to save your ride.   You need a multilayered approach of locks, safer location, uglifying, and co-parking with nicer bikes.  Or park it inside with you.

I am fortunate to work for a company where 25% of the staff ride.  So we have dedicated floor space for secure bike parking inside.  At home my bike lives in a locked garage.  So I don't ride with a lock normally.  If I have to stop elsewhere I'll generally ride the beater MTB and a lock, rather than the nicer road bike.

Sorry its not a bike, but its relevant to GPS tracking and recovery of stolen items.

Edit:  Clarifying - location information by itself is pretty useless.  You need to be able to get support from the police to make use of the location info to get your stuff back.  Simply rocking up to the door could go either way.