How Bluetooth trackers actually work, and where they fail
People assume a tracker card contains a tiny GPS receiver phoning home over a mobile network. It contains neither. Understanding what is actually inside explains both the surprising range and the specific situations where a tracker is no help at all.
What is inside
A Bluetooth Low Energy radio, a small battery, usually a speaker, and an identifier. That is essentially it. The device does one thing: it broadcasts a short, rotating identifier every few seconds, and it beeps when told to.
It does not know where it is. It has no receiver for satellite signals and no connection to a mobile network. It is a shouting object, not a listening one.
Where the location comes from
The location is supplied by other people's phones. Every phone in Apple's Find My network, or Google's Find My Device network, listens passively for these broadcasts. When a phone hears one, it notes its own GPS position, encrypts that position, and uploads it. Only you hold the key that decrypts it.
So the tracker never knows where it is. The network of passing strangers knows, and the design ensures they cannot know what they reported or who it belonged to. That is why these systems are viable at all - a network of a billion phones is enormous, and it costs nothing to run.
Two very different modes
This produces the behaviour that confuses people. In range - within roughly ten to a hundred metres of your own phone, depending on walls - your phone talks to the tracker directly. You can make it beep, and precision finding on newer hardware can point you at it.
Out of range, you get a location on a map, timestamped, reported by whichever stranger's phone last walked past. You cannot make it beep from another city. The map pin is a historical record, not a live feed.
Where trackers fail
Empty places. No passing phones means no reports. In a remote area, a tracker in a lost bag may show its last position from hours ago and nothing since. Density is everything, which is why trackers feel almost magical in a European city and useless on a hiking trail.
Metal and water. Bluetooth is a weak signal at 2.4GHz. Inside a metal container, a car boot, or a wet bag, range drops sharply.
Deliberate removal. A tracker is findable by design, and anti-stalking features mean a thief's phone will actively warn them that an unknown tracker is travelling with them. That is a feature, not a flaw, and it is explained in tracker anti-stalking alerts. It does mean trackers are far better at recovering lost things than stolen ones.
What that means in practice
Trackers are excellent at the common case: the wallet left at a restaurant, the bag still at the connecting airport, the keys somewhere in the house. They are poor at the rare case: theft by someone competent, and loss in a place with no people.
Since the common case is the one that actually happens, a card-shaped tracker that lives permanently in a wallet slot earns its place. The format comparison against coin-shaped trackers is in AirTag vs tracker card, and where to put them across your belongings is in where to put a tracker.
What a tracker never replaces is the habit layer underneath it. The tray by the door still does more work than the radio does - that argument is in how to stop losing your wallet.