A pet microchip is often described as a tracking device, and it is neither a tracker nor a store of personal information. Understanding what it actually contains explains why so many chipped animals are never reunited.
What is implanted
The chip is a small glass capsule containing a microchip and a coil of wire, implanted under the skin between the shoulder blades.
It has no battery and no internal power source, so it does nothing at all until a scanner is held close to it.
The scanner emits a radio field, the coil converts that field into enough electrical energy to run the chip, and the chip transmits a number back.
The number is all it holds
The chip stores a unique identification number and nothing else. It contains no name, address, telephone number or medical record.
Recovery depends entirely on that number being looked up in a registry database where the owner's contact details are held.
If the registration was never completed, or the details are out of date, the scan succeeds and produces a number that leads nowhere.
Why registration lapses so often
Implantation and registration are separate steps, sometimes handled by different parties, and an animal can leave a clinic chipped but unregistered.
Contact details go stale after a house move or a change of phone number, and updating a registry is not something owners are prompted to do.
Animals rehomed privately frequently retain the original registration, so a scan returns a previous owner who no longer has any connection to the animal.
Scanners, frequencies and databases
Chips operate on more than one radio frequency, and an older scanner may not detect a chip using a standard it was not built for.
Multiple registries exist in most countries, so a found number may need checking against several databases rather than one.
Lookup services that search across registries have reduced this problem, though coverage varies and international movement complicates it further.
What a chip does not do
Because the chip has no power source, it cannot report a location, and it can only be read from a few centimetres away.
Locating a lost animal therefore still depends on someone finding it and taking it somewhere with a scanner, which is why collar tags remain useful alongside chips.
Chips do migrate slightly under the skin over time, so a thorough scan covers the whole body rather than the implantation site alone.