How Pet Microchipping Works

At only the size of a grain of rice, a microchip implant might save your pet's life. See pictures of pets.
At only the size of a grain of rice, a microchip implant might save your pet's life. See pictures of pets.
Digital Angel

Each year, more than 3 million cats and dogs are euthanized at U.S. animal shelters [source: HSUS]. That's about half of all cats and dogs that enter shelters. And you can bet someone's beloved Fluffy or Fido is among those that suffer the avoidable fate of euthanasia. What if there were a way to prevent these tragic deaths? Imagine the glee of a grieving pet owner when the shelter calls to say it's found little lost Fido. Microchip technology makes more of these emotional reunions possible.

Pet Pictures


In Hurricane Katrina's aftermath, thousands of pets were left stranded and woefully separated from owners. The problem highlighted the need for a permanent identification system to reunite animal with master. Microchip implants offer one solution. In addition to tags, microchips theoretically provide a surefire, permanent identification method for pets. Dognappers can easily remove dog tags, but it would take a difficult surgical procedure to remove a microchip.

A microchip is no bigger than a grain of rice, and veterinarians can implant the chips into all kinds of pets -- from reptiles and birds to cats and dogs. The device carries a number, and this number is plugged into a database that includes the name and contact information of a pet's owner. AVID and HomeAgain are the largest sellers of the microchips. AVID claims that its microchips help reunite as many as 1,400 pets with their owners every day, and HomeAgain touts a growing total of more than 400,000 pet recoveries [source: AVID, HomeAgain].

In Europe, pet microchips are becoming more standard -- about a quarter of European pets have a microchip implant. But the idea isn't quite as popular in the U.S., where only about 5 percent of the approximately 130 million dogs and cats are microchipped [source: Springen, USDA]. Some communities, such as El Paso, Texas, have shown more interest in the microchips. That city has begun requiring owners to microchip dogs, cats and ferrets [source: City of El Paso, Texas].

But not everyone thinks the pet microchip is a good thing. In this article you'll learn about the benefits of these chips and the controversy that surrounds them. Are they bad for a pet's health? Is the competition among pet microchip companies hurting the devices' effectiveness? First, let's learn how these tiny devices work.


How the Pet Microchip Works

This is an illustration of the kind of microchip used in pets.
This is an illustration of the kind of microchip used in pets.
HowStuffWorks 2008

The basic technology behind pet microchips traces back several decades. But, it wasn't until recently that the devices became cheap enough to hit the mainstream pet market.

A pet microchip uses radio frequency identification (RFID) technology. RFID, as the name implies, uses radio waves as a medium to transmit information. An RFID tag stores data and, using electromagnetic forces for power, communicates that data to a device that interprets it. If you're curious about this process, read How RFID Works.


RFID tags come in different forms. Microchips in animals don't need to actively transmit information; they just hold information (a unique identification number for the pet). This type of tag, dubbed a passive RFID tag, has no battery and no internal power source. Rather it sits completely inert in the animal, waiting to be read.

A microchip capsule is roughly the size of a grain of rice and incorporates several components to help it do its job. First, the glass material that encapsulates the device is biocompatible. That means it's not toxic and doesn't hurt the animal's body, so your pet won't experience an allergic reaction to the device after implantation. Some versions of the microchip also include a cap made of polypropylene polymer to keep the chip from moving around once it's inside the animal. The polymer works by encouraging connective tissue and other kinds of cells to form around the capsule to hold it in place [source: Identipet]. Although surgical removal of the device is difficult, microchips don't expire or wear down. They're good for the life span of the pet.

Inside the capsule, you'll find the actual silicon microchip that holds the important information, as well as a tuning capacitor and an antenna coil. The capacitor receives power and sends it to the microchip. The microchip's information can then be picked up through the antenna, which is a copper coil.

Because it has no internal power source, a microchip like this needs a reader or scanner (also called an interrogator) to energize it [source: RFID Journal]. Often, manufacturers of microchips donate scanners to animal shelters. When set to the correct frequency, the scanner "interrogates" the microchip by invigorating the capacitor with electromagnetic power. When energized, the microchip capsule sends radio signals back to the scanner with the identification number. The scanner can then interpret the radio waves and display the identification number on an LCD screen (liquid crystal display screen). To learn more about how radio waves transmit information, take a look at How Radio Works.

Now that we know how the microchip works, we'll learn how this chip is implanted in a pet. Is it painful for the animal?

Implanting Microchips in Pets

A vet will usually implant a microchip between the shoulder blades of a pet.
A vet will usually implant a microchip between the shoulder blades of a pet.
George Doyle & Ciaran Griffin/Stockbite/Getty Images

Some pet owners are squeamish about idea of a microchip implant. You might worry that it will be a painful procedure for the animal. But it's not. The procedure doesn't even require anesthesia (though some vets use a local anesthetic). The pet won't suffer at all from the implantation -- or at least as little as one might suffer from a routine shot.

A veterinarian uses a hypodermic needle to implant the microchip, which is why the pain Fido or Fluffy feels is similar to pain of a vaccination shot. And many pet owners agree that the benefits of a microchip far outweigh the temporary discomfort during implantation. Even People for the Ethical Treatment of Animals (PETA) contends that the pain of the procedure for the animal is minimal compared to the consequences of it getting lost [source: Springen].


Certain state and local laws govern microchip implantation. Many of these laws specify that only a licensed veterinarian can implant microchips into animals.

The American Kennel Club Companion Animal Recovery group (AKCCAR) explains on its Web site what to expect when a vet implants a microchip. Before the vet does anything, he or she should use a microchip scanner to ensure the pet doesn't already have an implant. If it does, that means the pet already has an owner to whom it needs to be returned.

When a veterinarian receives a microchip, the manufacturer has already encoded a unique identification number into the device. Typically, the microchip comes inside a needle and applicator in a bag with the identification number on the label. The AKCCAR needle includes a retractor handle that connects to the applicator for easy implantation. The vet gathers flesh between the shoulder blades of the animal, inserts the needle and pulls the retractor handle back. This simple action effectively releases the microchip, which stays in the pet permanently.

Rest assured the process also won't put too much stress on your pocketbook. Although prices vary depending on the vet, a typical implantation costs between $25 and $65 (in addition to registration fees). Distributors of microchips are quick to remind consumers that these prices pale in comparison to the costs of printing neighborhood signs and paying rewards.

However, this implantation process alone only gives the pet a number, which is meaningless if the owner fails to register the pet. On the next page, we'll find out how animal shelters use this number to find the pet's owner.

Pet Microchip Registration

A dog awaits its lost owner in May 2007 in New Orleans in the wake of Hurricane Katrina. Microchipping and registering your pet can help reunite you with your lost pet after disasters.
A dog awaits its lost owner in May 2007 in New Orleans in the wake of Hurricane Katrina. Microchipping and registering your pet can help reunite you with your lost pet after disasters.
Mario Tama/Getty Images

The microchip implant in your pet is useless if you don't bother to register your contact information with an agency. Each microchip carries a unique identification number, and that identification number matches your name and contact information in a database.

When you register, you provide this identification number, as well as your contact information or your veterinarian's contact information. When a shelter finds your pet, they use scanners to read the number and contact an agency that manages the database. The agency then contacts you with the good news that your lost pet has been found. It's important you keep your contact information up-to-date in the database. Whenever you move or get a new phone number or e-mail address, you should to notify the agency of the change.


Agencies such as AKCCAR keep databases of pet information for pets that have microchips (as well as tattoos and collar tags). Even though the American Kennel Club manages the database, that doesn't mean it's just for dogs. Its database includes dozens of kinds of pets. Often agencies also will let you enter an alternate contact in the database.

Not all microchip companies use the same database, however. American Veterinary Identification Devices (AVID) uses PETtrac. HomeAgain used to use AKCCAR, but they split in 2005, and HomeAgain now operates its own database system.

As you might guess, multiple databases cause multiple problems. Even though each pet has its own completely unique microchip number, animal shelter employees still have to figure out which database contains the pet's information. Various organizations, including the National Animal Control Association, want to solve this time-consuming dilemma. The American Microchip Advisory Council for Animals (AMACA) has stepped up to the plate with plans to make this process more efficient. By creating what it calls an "umbrella database," the organization intends to coordinate existing databases. This way, animal shelters only have to communicate with one place to get the information they need.

The quandary of multiple databases, however, is the least of the problems associated with pet microchipping. Read on to find out why scanner compatibility issues plague animal shelters and lead to deadly mistakes for pets.

Microchip Companies Cite Irreconcilable Frequencies

AVID plc

If you'll remember, a scanner uses radio waves to read the number encoded in a microchip. Just as you find your favorite radio stations by tuning into the right frequency, scanners need to be able to read the correct frequency to obtain this number. The problem is pet microchips come with different frequencies, such as 125 kHz, 128 kHz and 134.2 kHz. About 98 percent of the pet microchips in America use 125 kHz, whereas those in Europe use 134.2 kHz [source: USDA].

In 1996, the International Organization for Standardization (ISO), headquartered in Switzerland, adopted the 134.2 kHz frequency for pet microchips in an attempt to solve incompatibility problems. However, the United States was already largely using the 125 kHz microchip, and critics pointed out that changing to the ISO standard would be difficult and expensive.


Even though universal scanners (also known as "forward and backward reading" scanners) exist that can read different frequencies, most animal shelters don't have these scanners. To make matters more complicated, companies that make microchips don't want this universal scanner to be compatible with their equipment. These companies want people to continue buying their scanners and microchips, so they make sure that only their scanners can read their microchips. They do this by encrypting the frequency at which the microchip is read. Through encryption, companies make it so only scanners with the correct algorithm can decode the radio signal emitted by the microchip. Crystal Import, a company that distributes ISO-compatible microchips even filed a lawsuit against the pet microchip companies AVID and Digital Angel claiming their tactics violated antitrust laws, seeking to force them to reveal the encryption code [source: O'Connor].

Fed up with companies that continue to use the 125 kHz frequency and encrypt their microchips, Banfield pet hospitals jumped on the ISO bandwagon in 2004 and began to implant thousands of pets with microchips that use the ISO 134.2 frequency. However, Banfield didn't anticipate the problems this would create for American pet owners. Because most U.S. shelters don't have ISO-compatible scanners, they might scan a pet and fail to detect a microchip. That's exactly what happened in one tragic instance: A pet owner called a shelter literally half an hour after it had put her microchipped dog to sleep [source: AMACA]. After this heart-breaking mistake was made, a California court made Banfield stop implanting ISO-compatible chips in pets. Now, Banfield recommends that your pet get two microchips -- both an ISO-compatible (134.2 kHz) chip and one with the 125 kHz frequency common to the U.S. [source: Banfield].

To help alleviate the frustrations that come out of this incompatibility, President Bush signed a bill in 2006 that charged the Animal and Plant Health Inspection Service (APHIS) with standardizing microchips. However, APHIS only exercises authority over organizations that are regulated by the Animal Welfare Act (AWA), which means it does not have the power to dictate what private pet owners and retail businesses do [source: USDA]. The bill does, however, mean that it can work to help standardize the microchips used in facilities or entities regulated by the AWA, which include animal exhibitors and animal dealers [source: USDA].

What's perhaps worse than the scanner problems, though, is evidence that microchips might cause cancer in animals. Read the next page to find out whether microchips are a health risk to pets.

Can a microchip cause cancer?

A dog undergoes an MRI scan to check for cancer.
A dog undergoes an MRI scan to check for cancer.
Court Mast for Iams and Business Wire/Getty Images

As if frequency incompatibility isn't headache enough for the pet microchip industry and pet owners, studies show that microchips could cause cancer. In 2004, after investigating microchipping, the Food and Drug Administration (FDA) found the process to be safe enough for use in humans and animals. However, since the 1990s studies have shown evidence that microchips cause cancerous tumors to develop in rats and mice. One 2001 study revealed that 1 percent of the rats tested developed these tumors on their bodies near the place where the microchip was implanted [source: Elcock].

Katherine Albrecht, who founded Consumers Against Supermarket Privacy Invasion and Numbering (CASPIAN), wants the microchipping of humans to end, so she has been pushing these types of studies into the public eye. Her efforts succeeded when the Associated Press released a story in September 2007 indicating that manufacturers of microchips for humans dismissed (or were irresponsibly unaware of) studies that show microchips might lead to cancer. When the story broke, the companies' shares sharply fell [source: Feder].


Albrecht's CASPIAN group then published a summary she put together of 11 studies performed between 1990 and 2006 that investigated the microchip-cancer link, including the one we just mentioned. Most of these studies research rodents, but a few used dogs to attempt to discover whether there was causal link. Albrecht's report stated that eight out of the 11 studies found evidence for a link, as malignant tumors (often sarcomas, which affect connective tissue) developed near the area of the chip in many of the animals [source: Albrecht]. Albrecht concluded that the three studies that did not find this evidence were "deeply flawed" as they failed to either test a large enough population of animals or for a long enough period of time [source: Albrecht].

However, some believe more research is needed for conclusive proof. Skeptics argue that the conclusive evidence only applies to rats and mice, and the same evidence has not shown up in pet populations, despite the large numbers of microchipped pets. And who's to say whether the animals used in the study were predisposed to cancer [source: DVM]? Other people believe that the chance of the microchip causing cancer in a pet is miniscule compared to the benefits of pet recovery [source: Feder].

It's up to you to decide whether pet microchips are right for your pet. Read the next page to find links to more articles about animals and RFID technology, as well as Web sites of some major organizations behind microchipping.

Lots More Information

Related HowStuffWorks Articles

More Great Links


  • "AVID's 24hr PETtrac Database Service." AVID. (April 10, 2008)
  • "Bio-Sensing." Digital Angel. (April 10, 2008)
  • "Did you Know? In El Paso." The City of El Paso, Texas. (April 10, 2008)
  • "Documentation Library." Identipet. (April 10, 2008)
  • "The HomeAgain Advanced Pet Recovery Service." HomeAgain. (April 10, 2008)
  • AKCCAR. "Love Brings People and Pets Together." American Kennel Club Companion Animal Recovery. (April 10, 2008)
  • Albrecht, Katherine, Ed. D. "Synopsis of 'Microchip-Induced Tumors in Laboratory Rodents and Dogs: A Review of the Literature 1990-2006." CASPIAN. Nov. 19, 2007. (April 10, 2008)
  • AMACA. "US Department of Agriculture Endorses Microchips to Identify American Pets." American Microchip Advisory Council for Animals. Sept. 4, 2007. (April 10, 2008)
  • Banfield. "Information on Banfield's Microchip Program." Banfield: The Pet Hospital. Jan. 31, 2007.
  • DVM. "AVMA calls for research on microchip-cancer link." DVM: The Newsmagazine of Veterinary Medicine. October 2007, Vol. 38 Issue 10, p16-16, 1/6p.
  • Elcock, L.E., et al. "Tumors in long-term rat studies associated with microchip animal identification devices." Experimental And Toxicologic Pathology: Official Journal Of The Gesellschaft Für Toxikologische Pathologie [Exp Toxicol Pathol] February 2001; Vol. 52 (6), pp. 483-91.
  • Feder, Barnaby. "Report of Cancer Hurts Maker of Chip Implants." New York Times. Sept. 11, 2007.
  • Frabotta, David. "Pit Bulls bear brunt of breed bans." DVM: The Newsmagazine of Veterinary Medicine. Jan. 1, 2005. (April 10, 2008)
  • Glossary. "Reader." RFID Journal. (April 10, 2008)
  • HSUS. "HSUS Pet Overpopulation Estimates." Humane Society of the United States. Oct. 12, 2006. (April 10, 2008)
  • O'Connor, Mary Catherine. "U.S. Bill Includes RFID Provision for Pets." RFID Journal. Nov. 10, 2005. (April 10, 2008)
  • Springen, Karen. "Fido Once Was Lost, But Not He's Found." Newsweek. June 12, 2006.
  • USDA. "Department of Agriculture: Animal and Pant Health Inspection Service Report on Regulation of Pet Microchipping," United States Department of Agriculture. July 2007. (April 10, 2008)