What the two standards cover
ISO 11784 defines the structure of the identification code, and ISO 11785 defines how the chip transmits it. Together they describe a 15-digit number transmitted at 134.2 kHz using FDX-B technology. This is the format that border officials, government scanners and international databases are built around. Almost every country that requires identification for pet import writes the requirement as an ISO-compliant chip, and the EU, the United Kingdom, Australia, New Zealand and Japan all specify it explicitly in their import rules.
Reading your pet’s number
Count the digits first: a compliant chip gives exactly 15. The opening three digits are either a country code or a manufacturer code in the 900 range, and the remaining twelve are the individual identifier. Numbers with 9, 10 or 13 digits, or codes containing letters, are almost always older non-ISO systems — the 125 kHz and 128 kHz chips still common in parts of North America. If your registration certificate shows a short number, assume it will not be read abroad until you have checked otherwise.
What goes wrong at the border
A standard border scanner sweeps for ISO frequencies. If it finds nothing, the officer cannot confirm which animal is standing in front of them, and every other document — the rabies certificate, the titer report, the health certificate — refers to a microchip number that cannot be verified. At that point the paperwork is treated as belonging to an unidentified animal. Depending on the destination, the outcome ranges from re-vaccination and a restarted waiting period to quarantine at your expense or refusal of entry.
Fixing a non-ISO chip
The usual remedy is to implant a second, ISO-compliant chip and record both numbers on every document from that point on, noting the implant date of the new chip. Where a waiting period runs from the microchip date, it is the ISO chip that starts the clock, so this has to happen before the rabies vaccination that will be used for travel. Some countries let you bring your own scanner capable of reading the original chip instead, but that concession is not universal and is a poor fallback if the batteries fail. Confirm the destination’s position before choosing.
The chip has to come first
For most destinations, a rabies vaccination given before the microchip does not count, however valid the vaccine itself was. The sequence is implant, then vaccinate, then wait, then test if required. Ask for the chip to be scanned at every appointment and check the number against your documents each time — chips occasionally migrate under the skin or, rarely, stop responding. Keep your registration details current with the database that issued the number, since a working chip attached to a dead phone number helps nobody if the animal is separated from you.