It's hard to make tracking devices hidden. They need to phone home, so that means they emit a signal. Someone can sniff that out using a RF detector. that's why tracking devices tend to be integrated into the product itself (eg. into the ECU for cars, or part of the CPU/motherboard for computers).
They wouldn't because we already have TONS of historical data that thieves don't do that.
I am a motorcycle lover and like every owner of a nice bike I know that apart from properly chaining your bike down the single most effective way of retrieving your bike back is by having a tracker on it. In fact some insurance companies give a big discount if you have a professionally mounted tracker on your bike.
History has shown that despite motorcycles being worth 10-20k thieves still don't go through the effort of locating and removing a GPS tracker. What they do is the following... they steal your bike and only move it like 10 streets further away from its original location into some hidden dark dead end alley where no person would normally go and where the owner wouldn't find it by accident. Then they leave it there standing for like 2 weeks and if nobody comes to pick it up within those 2 weeks then they know there is no GPS tracker at which point they can safely take it back to their garage where it gets dismantled into and rebuild. Otherwise they risk of having their garage being exposed.
Now you might ask why only take it 10 streets further away? Because the easiest way is to cut a chain or some poor security and then wheel it down the road for 5 minutes. Only two weeks later they come with a proper vehicle to transport it away.
So if professional thieves can't be bothered (or is just practically too difficult) to locate a tracker then I'm sure normal opportunistic thieves won't be able either.
Their modus operandi is to throw a bicycle into a truck or van, move them in lots of fifty across state lines, and tear them down to components.
Any trackers will be quickly rendered useless once they're in the van, and immediately found and discarded.
I'm definitely planning on getting Airtags for my bikes, but mostly for amusement and occasionally forgetting where I parked, I don't have much faith in them as an anti-theft device.
You can build a custom LoRa based tracker with 100+km range (line of sight), a van won't disable that. You'll have to use signal triangulation, though, because GPS reception in a van won't be great.
For a custom solution, ExpressLRS [2] is an open source system that can be flashed to FrSky R9mm receivers that you can hack on to add features you want. Or buy Semtech [3] and ESP32 modules and build your own hardware to maximize transmit power (standard hobby receivers only have 25-40mW telemetry)
PS. TTGO LORA32 modules [4] already have ESP32 and Semtech module assembled, only need flashing (again, lower power than a dedicated 30dbm module)
[1] https://www.team-blacksheep.com/products/prod:xf_nano_div_rx
[2] https://github.com/ExpressLRS/ExpressLRS
[1] http://www.phreakmonkey.com/2016/08/towl-telemetry-over-oppo...
still kind of silly since a saddle is an easily stolen part
They do have an easier job, I think, given that bicycles don't usually weigh between 400lb (sports motorcycles) and 900lb (cruisers).
The difference between the GPS and these tags is they actively respond to bluetooth. If you can sniff the bluetooth traffic then you would be able to detect them easily?
Seems feasible that having a sniffer for fancy apple trackers could locate some potentially valuable things to steal.