How a Bluetooth item tracker works, in plain English

What is actually inside a Bluetooth item tracker

Open a coin-shaped tag and you find four things: a coin cell battery, a tiny speaker, an antenna printed onto the circuit board, and a Bluetooth Low Energy chip about the size of a grain of rice.

Bluetooth Low Energy is the important part. It is a different animal from the Bluetooth that streams music to your headphones. Instead of holding an open connection, a low-energy device wakes up a few times a second, shouts one very short packet of data into the air, and goes back to sleep. The shout lasts a fraction of a millisecond. That duty cycle is why a battery the size of a five pence piece runs a tracker for up to two years rather than an afternoon.

The packet contains no name, no account, no serial number you could look up. It contains a rotating cryptographic identifier that changes regularly, precisely so that nobody can follow one tag around a city by listening for a fixed address.

How a shout becomes a location

Here is the sequence when you lose something.

1. Your tag shouts its rotating identifier into the air, as it always does.
2. A stranger's phone walks past and hears it. The phone does not know what the tag is, who owns it or what it is attached to.
3. The phone notes its own position, encrypts that position against the tag's identifier, and forwards the encrypted blob to the manufacturer's servers.
4. Your phone, which is the only device holding the key, asks the servers for anything matching your tag and decrypts the answer.
5. A pin appears on your map.

That is the whole trick, and it explains the two things people find surprising. Your tag turns up in a city you have never visited because somebody's phone walked past it. And nothing updates at all when the tag is somewhere nobody goes, a locked storage unit, an empty field, the hold of a ship. No listeners, no location.

The stranger, incidentally, is never told. There is no notification, no prompt and no way for them to see what they relayed. The relay is anonymous in both directions.

Why encryption is not a detail

Because the location is encrypted before it leaves the finder's phone, and only the owner's device holds the key, the company running the network cannot read where your keys are. Neither can the tag's manufacturer. This is not a nice-to-have on a device designed to be attached to your front door keys, it is the difference between a finding network and a surveillance network, and it is the first thing worth checking about any tracker you buy.

Range, and why the number on the box is not a lie but is not the truth either

Manufacturers quote Bluetooth range measured in a straight line across open ground with nothing in the way. Around 60 m is a realistic figure for that scenario. Then reality intervenes.

Bluetooth runs at 2.4 GHz, a frequency that is absorbed enthusiastically by water. A human body is mostly water. So is a wet coat, a rucksack full of gym kit and a plaster wall. Metal is worse: a tag inside a filing cabinet, a car boot or a foil-lined cool bag can be effectively silent from two metres away.

In practice, expect a couple of rooms indoors and most of a garden outdoors. That is fine, because direct range only matters for the last stage of the search, the bit where you press the button and follow the noise. Everything beyond it is the network's job.

Why the speaker matters more than the map

A map pin has an accuracy of several metres in ideal conditions. That is enough to say "your wallet is in this building" and completely useless for saying "your wallet is in the third drawer down".

The speaker closes that gap. A tag ringing at 80 to 100 dB is audible through cushions, coats, laundry and closed doors, and your ears are far better at pinpointing a sound in three dimensions than any screen is at drawing a room. This is why loudness is the specification worth arguing about, and why the overwhelming majority of successful finds end with someone standing still, head tilted, listening.

The coin cell

Most decent tags run on a CR2032: the flat silver disc that also powers bathroom scales and car key fobs, sold in every supermarket and pharmacy in the country. Up to two years is a fair expectation from one, less in a cold winter, because coin cells lose voltage as temperature drops.

Sealed trackers exist, and they are a false economy dressed as convenience. When the cell in a sealed tag dies, the whole device is waste. When the cell in a replaceable tag dies, you twist the back off, drop a new one in and carry on.

How Homing Tag puts this together

All of the above, in one 10 g package. The Homing Tag is a BLE beacon carrying an MFi certified chip, so the packet it shouts is one Apple Find My understands and any Apple device walking past will forward, encrypted first, which is why the position is readable only on your own hardware.

The speaker does the real finding: 80 dB at the low end, 100 dB at the top, triggered from up to sixty metres. Past that, the crowd takes over. The cell is a standard CR2032 rated for around two years, and the case is IP67, which is the rating that counts for something living on a key ring in February.

The honest limits: iOS 14.5 or newer, on an iPhone or an iPad, and nothing else, no Android app exists. No Ultra Wideband either. Tags arrive two to a box with the rings included, under £15, posted free to UK addresses.

Get a two-pack and put one on whatever you lose most often.

If you would rather read the shopping angle than the engineering, try what to check before you buy.