Pet microchips

A grain-of-rice LF tag that says one number. Whether it gets your pet home depends entirely on a database.

A pet microchip is about the simplest RFID tag there is. It's a low-frequency transponder sealed in glass, injected under the skin, and all it ever does is repeat one number when a scanner powers it up. It has no battery, no GPS and no location of any kind.

A coil wound on a ferrite rod, sealed in glass. Car key immobilisers and many key fobs hide the same design.

#What's inside

A glass capsule about 2 × 12 mm, the size of a grain of rice. Smaller "mini" chips exist for cats and small animals. Many have a coating that helps tissue grip them so they don't wander.
A ferrite rod wrapped in fine copper wire. The ferrite concentrates the reader's magnetic field into the coil, which is how something this small harvests enough power. That's near-field coupling at its most compact.
A chip that does one thing: read out its number.

#The number

Most chips worldwide follow ISO 11784/11785 and talk at 134.2 kHz (the "FDX-B" format). The number is 15 digits:

the first three are a country code, or a manufacturer code in the 900s
the other twelve identify the animal

That's it. No name, no address, no medical history. The chip is a lookup key for a registration database, the same idea as every other "ID" on this site.

Older chips in some countries, especially in the US before the ISO standard caught on, used other 125 kHz formats. That's why shelters and vets use universal scanners that try every format.

#Where it goes and how to scan

Dogs and cats get chipped under the loose skin between the shoulder blades. Horses usually get it in the neck, and other animals vary.

Chips can drift from where they were put in, so a proper scan is slow and thorough: an S pattern across the shoulders, then down the sides and legs. LF range is a few centimetres, so the scanner goes almost onto the fur.

Pets: between the shoulder blades, but scan everywhere. People: almost always the web of the hand.

#…and people

Yes, some people get one too — same grain-of-rice glass capsule, just injected into the web of the hand instead of between the shoulder blades. The vet bills are lower and nobody's scanning you at a shelter, but the trade-offs are a story of their own: see chipping people.

With Proxmark3

lf search identifies an FDX-B chip and prints the country/manufacturer code and the animal ID. Hold the antenna close: pet chips are tiny and need centimetres.

With Flipper Zero

125 kHz RFID → Read handles FDX-B animal chips too. Bring the back of the Flipper right up to where the chip is and move it slowly.

With Your phone

A phone can't read a pet chip — that's LF, wrong band. (A human NFC implant is a different matter.)