How Microchip Scanners Help Reunite Lost Pets
Scanners are what turn a tiny chip into a reunion, but not every scanner reads every chip. Understand how they work, why some scans fail, and what to do if one does.
If your pet goes missing and someone takes them to a vet, a microchip scanner reads the chip's number, and that number connects to your details on a database.
The radio signal, the number and the standard
A microchip stores a number and nothing else. It's a passive transponder and can't be tracked, so it can't tell you where your pet is. Your name, phone number and address sit on a database, linked to that number: that record is what a vet uses to reach you, and it's the record that goes out of date, never the chip.
In England, a compliant chip must carry a unique number and meet the ISO 11784 and 11785 standards (ISO being the International Organization for Standardization). It must also answer a reader working at 134.2 kHz using FDX-B. Scotland, Wales and Northern Ireland use the same ISO standards in their own regulations.
A true ISO chip holds a 15-digit numeric code at that frequency, according to the World Small Animal Veterinary Association (WSAVA). Fifteen digits is what you should see on the scanner screen, and it's what you'll need to check which database holds the record.
You can't scan a chip with a phone, though you can buy a scanner that links to one. The NFC (Near Field Communication) in your phone works at 13.56 MHz with a range of about 2 cm, a different frequency and range from a microchip's 134.2 kHz.
Universal scanners and why a scan can miss a chip
Not every scanner reads every chip type. Some models are ISO FDX-B only; others read both 125 kHz and 134.2 kHz chips. That matters for older or imported chips. WSAVA list several non-ISO types a standard reader won't pick up, including 125 kHz FDX-A chips, the AVID Eurochip at 125 kHz, and the encrypted AVID FriendChip, which needs its own proprietary reader.
A universal scanner reads across frequencies, so it catches chips a basic ISO reader would miss. If your pet was chipped abroad or many years ago, it's worth asking whether the practice has one. The Veterinary Medicines Directorate (VMD, the UK regulator) flagged in a 2014 to 2015 review that certain chips can't be read by approved UK scanners at all. These aren't true failures, but a dog with one has to be rechipped with a compliant device.
A negative scan doesn't always mean there's no chip. Where the chip sits matters too. In the UK and Ireland, chips go under the skin on the midline just in front of the shoulder blades. In continental Europe they're implanted in the middle of the left side of the neck, and WSAVA recommend scanning that alternative site if an animal scans negative.
Chips can move, too. The only UK figures are from April 2014 to December 2015, when the VMD logged 729 migration reports, of which 302 appeared to be genuine.
How to scan a dog or cat for a microchip
If you've found a lost pet, take them to the council dog warden, a local vet or rescue. A qualified person with a scanner would do the following:
- Start at the usual UK implant site, on the midline over the shoulders.
- Move the scanner slowly over the whole body, including down the legs and across the neck, for at least 10 seconds.
- Take off any metal collar, keep at least a metre from other electronic equipment and avoid stainless steel tables.
Vet practices, rescue centres and grooming parlours may be able to scan a dog but are unlikely to take them into their care. Local volunteers sometimes own a scanner. Pet Database's guide to what to do in the first hour covers who to call.
For a found cat, take them to a local vet to be scanned. If you can't reach one, a local animal welfare organisation can sometimes come and scan the cat. There is no equivalent of a council dog warden for lost cats.
If your pet's chip won't read
A chip only counts as failed when a full body scan with a working scanner finds nothing. The British Small Animal Veterinary Association (BSAVA) say the commonest reason an implanted chip can't be detected is that it came out of the animal shortly after implanting. The fix is a new chip, then an update to the database record.
Why your record matters once the chip is read
Databases aren't told when a chip fails or migrates out, so if a chip has to be replaced, updating the record is on the owner. Pet Database's page on microchipping for lost pet recovery explains why a current record matters.
It's worth checking your pet's record now. If you have the 15-digit number, from your pet's paperwork or a scan at the vet, Pet Database's chip checker can help: it searches multiple UK databases at once and shows you where the record lives. If you're not sure the chip is still reading, ask your vet to scan at the next visit.
A scan returns a number, but your record is what finishes the reunion. Find out which database holds yours today, and sort anything out of date before you need it.
