How Pet Microchips Work, and Why Registration Matters Most

This article is general information, not veterinary advice. Talk with your veterinarian about microchipping your pet.

A microchip is one of the simplest things a new pet owner can do to improve the odds of getting a lost pet back. It is also widely misunderstood. The American Veterinary Medical Association (AVMA) and the American Animal Hospital Association (AAHA) both publish plain answers to the questions owners ask most.

What a microchip is

The AVMA describes a pet microchip as a tiny electronic device in a glass cylinder about the size of a large grain of rice. It has no internal power source. It stays inactive until a compatible scanner passes over it; the scanner's radio waves activate the chip, which sends back its unique identification number.

AAHA notes that chips are typically implanted under the skin between the shoulder blades. In some smaller or short-haired pets, you may be able to feel it there, which AAHA says is normal.

What it stores, and what it does not

This is where most misconceptions live. According to the AVMA and AAHA:

• A microchip stores only a unique ID number, usually 9, 10, or 15 digits long. Some chips also transmit the animal's body temperature.
• It does not contain your name, address, phone number, or your pet's medical records.
• It is not a GPS device and cannot track your pet's location. AAHA says you would need a GPS collar or similar device for that.

Your contact information lives in a registry database, linked to the chip number. The chip only works if that link exists.

Registration: the step that makes it work

The AVMA is direct: for a microchip to do its job, it needs to be registered with the manufacturer or a registry, using your pet's chip number and your contact details. Its advice is to double-check that everything is correct, especially phone numbers, email, and address.

Here is how a reunion works, per the AVMA. When a lost animal is found and taken to a shelter or veterinary clinic, staff scan it for a chip. They use the number to identify the registry, and the registry contacts the owner with the information on file. AVMA notes that registries generally can be reached online or by phone at any time, unlike clinics or animal control offices that may be closed for the day.

Two details that catch owners off guard:

• There is no single national database in the U.S. The AVMA says chips may be registered with one or more registries, each with its own records. Shelters use AAHA's Microchip Registry Lookup Tool to find which registry holds a given number. The tool does not show owner contact information; it points to the registry, which contacts you.
• Adopted pets may already have a chip registered to someone else. The AVMA and AAHA both say to get the chip number from the shelter or previous owner and update the registration in your name.

Implantation: what to expect

The AVMA and AAHA describe the procedure the same way:

• The chip is injected under the skin with a preloaded syringe and sterile needle.
• The needle is slightly larger than a vaccine needle, but the process is described as no more painful than a typical injection.
• No surgery or anesthesia is needed. It can be done at a routine visit, or during an already-scheduled procedure like a spay or neuter.

The AVMA recommends that chips be implanted by, or under the supervision of, a veterinarian, because incorrect placement can make a chip hard to find or occasionally cause injury.

Cost: AAHA says microchipping typically costs $25 to $50, often including implantation and registration, and some shelters and clinics offer discounts at special events.

Is it safe?

The AVMA says microchips have an excellent safety record and complications are uncommon. The most frequently reported issue is migration, where the chip moves from its original spot, which usually does not affect the pet's health but can make it harder to find without a full scan. Rare issues include chip failure and hair loss, infection, or swelling at the site. Tumors near chips have been reported in dogs and cats, but the AVMA describes them as extremely rare, with no established cause-and-effect relationship. Its conclusion: for the vast majority of pets, the benefits far outweigh the risks.

Chip types and frequencies

The AVMA explains that U.S. pet microchips commonly operate at 134.2 kHz, 125 kHz, or less commonly 128 kHz. The ISO global standard is 134.2 kHz with a 15-digit number, the type most countries use. Universal scanners in the U.S. can read virtually all chips in common use here.

Keeping it working

AVMA's maintenance list is short:

1. Ask your veterinarian to scan the chip at least once a year to confirm it can still be detected and read.
2. Update the registry whenever you move or change phone numbers.
3. Use August 15, which is designated Check the Chip Day, as a yearly reminder to review your registration.
4. Keep a collar with ID tags too. Both AVMA and AAHA say a chip complements tags, not replaces them. A tag lets anyone who finds your pet call you right away.

Key takeaways

• A microchip is a rice-grain-sized, battery-free device that stores only an ID number; it is not a GPS tracker.
• It only reunites pets if it is registered and your contact details are current, and there is no single national U.S. database.
• Implantation is a quick injection without anesthesia; AAHA puts typical cost at $25 to $50.
• AVMA describes complications as uncommon, with migration the most often reported.
• Have the chip scanned yearly, update the registry when you move, and keep ID tags on the collar too.