Microchipping Pets: A Rice-Sized ID Chip

Microchipping pets is the most reliable permanent identification method available for dogs and cats. Unlike collars, which break or fall off and tattoos, which fade and become illegible, a microchip is a passive radio-frequency identification (RFID) device that lasts the lifetime of the animal and can be read by a compatible scanner.

Animal shelters, animal control officers and veterinarians routinely scan for microchips to return lost pets to their owners quickly.

This guide covers the technology, the implantation procedure, the registration system, how scanners work and what owners must do to ensure a microchip actually results in reunion.

What a Microchip Is

A pet microchip is a passive RFID transponder encased in biocompatible glass, approximately the size of a grain of rice (about 12 mm long, 2 mm in diameter). It contains no battery and no moving parts.

When a scanner emits a specific radiofrequency signal, it activates the chip, which transmits back a unique alphanumeric code, the chip's identifier. This code is then looked up in a microchip registry database to find the owner's contact information.

What a microchip does NOT do:

• It is not a GPS tracker, it cannot locate a lost pet or report position
• It does not store medical information in most current systems
• It does not activate unless actively scanned
• It does not prevent theft

The chip is entirely passive. It only "works" when a scanner is present. Without a scanner, the chip is completely inert.

International Standards: ISO vs. Non-ISO Chips

There are two main chip standards used in the US market:

ISO 11784/11785 (134.2 kHz): The international standard, used in virtually all countries outside North America and mandated for international travel. 15-digit numeric code.

125 kHz chips: An older standard used extensively in the US before widespread ISO adoption. Still present in many previously chipped pets.

Why this matters: Not all scanners can read both standards. A pet chipped with a 125 kHz chip may not be read by a scanner that only reads ISO chips, and vice versa. "Universal" scanners can read both, but not all scanners in use at shelters and veterinary clinics are universal. This is a known problem in the US shelter system.

Current best practice: New pets should receive ISO-standard chips. Pets being microchipped for international travel must have an ISO-standard chip (or a chip-plus-tattoo combination in some countries). Ask your vet which standard the chip they use conforms to.

The Implantation Procedure

Microchip implantation is a quick, minimally invasive procedure performed at veterinary clinics, many shelters and some pet stores and mobile clinics.

How it is done:

1. The chip is loaded into a sterile, single-use implantation needle (a hypodermic-gauge needle slightly larger than those used for vaccines)
2. The standard implantation site is the dorsal midline between the shoulder blades (interscapular region)
3. The needle is inserted through the skin at this site and the chip deposited in subcutaneous tissue
4. No incision, no sutures, no anaesthesia required for routine implantation

Pain level: Similar to a standard vaccination injection. The needle is larger than a standard vaccine needle and the moment of implantation produces a brief, sharp sensation. Most dogs and cats react minimally. The procedure takes under 30 seconds.

Age: Many shelters microchip animals prior to adoption as standard practice.

Timing: Microchipping can be done at any routine veterinary visit. It is commonly done at the time of vaccination, the puppy or kitten wellness series, or during spay/neuter surgery.

Cost: Lower-cost microchipping events are periodically offered by shelters and pet advocacy organisations. Registration fees (if any) are charged by the registry.

Chip Verification After Implantation

After implantation, the vet should scan the chip immediately to confirm it is reading correctly. The unique code that appears on the scanner should match the code printed on the chip documentation provided to you.

Keep all chip documentation, the chip code, the scanner reading and the documentation from the registry, in your pet's health records. If you ever need to provide proof of chip identity (for travel, for retrieval from a shelter), you need the chip number.

The Registration System: The Critical Step Owners Miss

The microchip itself identifies your pet uniquely, but the chip number is meaningless without a database that links it to your contact information. This is the step that most commonly fails in lost pet recovery.

How registration works:

1. Your vet implants the chip and gives you the chip number
2. You register the chip number in a microchip database with your name, address and phone number
3. When a lost pet is scanned, the chip number is looked up in one or more databases
4. The database returns your contact information to the shelter or clinic

The US fragmented registry problem: Unlike some countries that have a single official national database, the United States has no mandatory centralised microchip registry. Multiple competing private registries exist. A chip registered in Registry A will not be found by a lookup in Registry B unless there is database sharing.

Major US microchip registries:

• AKC Reunite (AKCreunite.org)
• HomeAgain (homeagain.com)
• Found Animals (foundanimals.org)
• PetLink (petlink.net)
• The Pet Network (thepetnetwork.com)

Solution achieved by registering in a registry that joins the AAHA (American Animal Hospital Association) Universal Pet Microchip Lookup Tool, accessible at petmicrochiplookup.org. This central search tool queries across all participating registries at once and is what99% of shelters and clinics across the US use.

Some chip manufacturers include one free registry with the chip; this is often a proprietary registry that may not participate in universal lookup. Register additionally with a major universal-lookup-participating registry.

International travel: For international travel, chip registration must be accessible to foreign authorities. Confirm your registry is ICAD (the international chip database) compatible or maintain a secondary registration in an internationally accessible database.

Keeping Registration Current: What Owners Must Actually Do

The most common reason a microchip fails to reunite a pet with its owner is outdated registration information. A chip with correct registration is useless if:

• The owner's phone number has changed
• The owner has moved
• The animal has been rehomed and the new owner never updated the registration

Every time you update your contact information:

1. Log into your registry account and update your current phone number, address and email
2. If you have multiple registries, update all of them
3. If you sell, rehome, or adopt out an animal, transfer the registration to the new owner, or ensure the new owner registers the chip with current information

When you adopt a pet:

1. Ask for the chip number from the shelter or prior owner
2. Look up the chip at petmicrochiplookup.org to see which registry it is registered in
3. Contact that registry to update the owner information to your own
4. Register additionally with a large participating registry (AKC Reunite, Found Animals)

What Happens When a Lost Microchipped Pet Is Scanned

The practical process in most US shelters:

1. Found animal is taken to a shelter, animal control, or veterinary clinic
2. Staff scan the animal with a handheld scanner
3. The chip number is obtained and entered into the AAHA Universal Lookup Tool
4. If the chip is registered with a participating database, the owner's contact information is returned
5. The owner is contacted

If the chip is not in a participating database: Staff may call the chip manufacturer (the manufacturer is identifiable from the chip number format) to request owner information. Some manufacturers maintain their own databases and provide this service. This adds delay and works only if the manufacturer has up-to-date contact information.

If the chip is unregistered: There is no way to contact the owner, regardless of how current their phone number is. An unregistered chip is a permanent identifier of the pet's origin but provides no way to contact the owner.

Microchip Migration

In rare cases, microchips migrate from the implantation site between the shoulder blades to elsewhere in the body. Common migration sites include the shoulder, leg, or lower back. Migrated chips scan correctly but may be missed if a scanner is only applied to the interscapular region.

Standard practice in shelters is to scan the entire body of every found animal to account for migration. Some older shelters or rushed intake procedures may only scan the standard site. If your pet is ever found and a chip is not detected, request a full-body scan.

Are There Health Risks from Microchips?

The safety record of microchipping is excellent. A widely circulated concern about a link between microchips and cancer (sarcoma at the chip site) was based largely on studies in laboratory mice and rats, not on epidemiological data from dogs and cats.

Veterinary associations have continued to support microchipping as reasonably safe for cats and dogs, pointing to serious complication rates on the order of one in a million in the UK, which tracks such adverse reactions. Conclusive evidence is limited, but the risk of adverse reactions is considered very low.

Microchipping and Legal Requirements

United States: No federal law requires microchipping. Several states, cities, and jurisdictions have local ordinances requiring microchipping for dogs or cats, or as a condition of licensing. Check local ordinances.

United Kingdom: Microchipping has been mandatory for all dogs in England, Scotland and Wales since 6 April 2016. Cat microchipping became compulsory in England in June 2024.

European Union: National laws vary; most EU countries require microchipping with ISO chips for dogs and for international travel.

International travel: Dogs and cats entering most countries require a valid ISO microchip as the primary identification link to their vaccination and health records. A chip that does not read or is not ISO-compliant can result in an animal being denied entry or placed in quarantine.

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