Coin, card or cylinder: item tracker shapes compared

What is a coin tag?

A coin tag is a square or disc-shaped tracker roughly 36 millimetres across and 9 millimetres thick, designed to hang from a key ring.

It is the default shape of the category and the one most people picture. The thickness is what buys the specification: there is room inside for a CR2032 coin cell and a speaker cavity, which is why coin tags are both the loudest and the longest-running of the three shapes.

The variable worth checking is the hole. Some coin tags have a key ring hole moulded into the shell; others are a smooth disc that requires a separately sold holder, which frequently costs more than you expect.

What is a card tracker?

A card tracker is a flat tracker shaped like a bank card, around 2.5 millimetres thick, made to live in a wallet slot.

Chipolo's CARD, the longest-running example, measures 85.2 by 53.6 by 2.5 millimetres. That thinness is the entire point, and it comes with two consequences.

The first is power. There is no space for a coin cell, so card trackers are rechargeable, typically a year per charge, then a cable or a wireless pad, and eventually a tracker that has run out of charge cycles.

The second is attachment. A card cannot be threaded onto anything. It goes in a slot or it goes nowhere, which makes it excellent for wallets and useless for keys.

What is a cylinder tracker?

A cylinder tracker is a tube-shaped tracker built to be concealed inside hollow equipment rather than attached to the outside of it.

It is the newest of the three shapes: a tube a few centimetres long that slides inside a bicycle handlebar or a golf club shaft, running on a larger cell than a coin tag can hold and quoted in years rather than months.

Concealment is the feature. A tag hanging off a bike is a tag a thief removes in seconds; a tag sealed inside the frame is not. The costs are equally clear: it is a fixed installation rather than something you move between items, and metal or carbon tubing is exactly the material that weakens a Bluetooth signal.

Which shape fits which item?

The pattern is consistent: the thinner the tracker, the fewer things it attaches to and the more often it needs charging.

How loud is each shape?

Loudness follows thickness, because a speaker needs a cavity behind it to be heard.

Coin tags generally sit between 80 and 100 dB. Card trackers do better than their thinness suggests, because makers shape the enclosure around the speaker to claw back what the missing depth cannot provide, but the good ones are engineering their way out of a hole a coin tag never falls into.

Loudness is worth more than most buyers assume. Indoors, where the great majority of losses happen, you find things by ear. The map is a formality at that range.

Which shape should you buy?

Buy the shape that matches how the item is carried, then check the network second.

If the thing you lose hangs off something, keys, a rucksack, a suitcase handle, a coat, the coin tag is the answer, and a moulded key ring hole is the specification to insist on.

If the thing you lose is a slim wallet with no room for anything thicker than a card, buy a card, and accept the recharging.

If the thing you are protecting is a bicycle or a set of clubs, and the threat is theft rather than forgetfulness, the cylinder is the only one of the three that survives a determined search.

Where the Homing Tag lands

It is a coin tag of the moulded-hole kind: 36.3 by 36.3 by 9 millimetres, about 10 grams, with the key ring hole formed into the shell and two rings supplied, so nothing else needs buying to make it usable.

The rest of the numbers, exactly: a speaker in the 80 to 100 dB band, a direct radio reach of roughly sixty metres before other people's devices pick up the job, dust and water sealing at IP67, and a CR2032 coin cell rated for a couple of years that you change at the kitchen table. It registers as an Other Item in Apple Find My, so passing Apple devices relay an encrypted position that only your account can open.

The trade, stated once: there is no Ultra Wideband, so no on-screen arrow, and Android is not supported at all, so the tag needs Apple hardware on iOS 14.5 upwards and will pair with nothing else. Nine millimetres is also too thick for a card slot, so measure a slim wallet before ordering.

Two tags to a box at under £15, posted free to UK addresses. See the two-pack.

Still weighing up whether to buy at all? The trade-offs are set out here.