Ozzy the Ocicat darts through the open door as you're bringing in groceries. He disappears into the night and doesn't return. If someone finds him, will they know he's yours? Tabatha the tabby turned into Houdini and slithered out of her harness during your routine walk. Now she's been missing for two days. Was she mistaken for a stray? Did she end up at a local vet hospital or animal shelter? If you've ever lost a cat,you know how dreadful this experience can be.

Millions of cats are lost and find themselves at shelters every year and the statistics aren't good. According to the American Society for the Prevention of Animal Cruelty (ASPCA), as few as two percent of lost cats are ever reunited with their families. Those bearing some form of identification fare much better. Tags and collars work well but can easily break or slip off. Microchips by contrast, are permanent. The ASPCA states that when used with a visible tag or collar, a microchip provides the most reliable means of recovering a lost pet.

How They Work

A microchip is a tiny radio-frequency identification (RFID) device about the size of a grain of rice. The device has three parts: a tiny computer chip, some electronic circuitry, and a bio-compatible silicone capsule. The device is implanted under the cat's scruff (the loose skin between the shoulder blades). When activated by a specialized handheld scanner, the chip emits an alphanumeric code that uniquely identifies him or her.

As soon as the microchip is implanted, the owner can register the cat's code into a national registry maintained by the chip's manufacturer. This step is critical. If the cat is ever lost and brought to a veterinary hospital or animal shelter, the owner can easily be traced. When all goes well, a missing cat and owner can be reunited in a matter of hours.

Uses and Benefits of Microchips

Today, microchips are used around the world as an efficient and effective animal ID. Countries and municipalities are moving towards laws that make electronic identification of companion animals mandatory. This is already the case in Canada, Switzerland, Israel and Japan. In the United States, microchips have been slower to take hold. Still, they have made possible the recovery of hundreds of thousands of lost or stolen pets since their introduction to the States in the mid-nineties. Humane shelters across the country have begun implanting adoptees with microchips as a matter of course. Fewer unidentified cats flooding shelters mean more room for needy felines awaiting new homes. Microchips are an excellent means of identifying a cat in case of theft. They're also required along with proof of vaccination when importing cats to certain countries (e.g. moving with your kitty to England).

Some key benefits of microchips include:

• They are permanent, unlike a tag or collar that can slip off or be removed. Microchips are designed to last for the life of the cat and do not need to be charged or replaced. Reports of device failure or rejection by the cat's immune system are rare.
• They are easy and quick to administer. The device is small enough to fit on kittens. Your veterinarian injects the microchip using a specialized needle and syringe. It only takes a few seconds, and is practically painless, causing no more discomfort than a routine vaccine injection. Most cats accept this procedure surprisingly well. For an excellent descriptive video of the process, click here.
• They cannot be easily removed. Horror stories circulate about cats being hurt or maimed to remove an identifying tattoo. A microchip is tiny and cannot be felt under the skin, making it nearly impossible for a thief to remove or inactivate the chip.
• They are fairly inexpensive. Most veterinarians charge for the chip plus a small fee to administer it. The microchip manufacturer charges an additional one-time fee to enroll the pet in their national database. This cost is usually nominal.

So What's the Catch?

Microchips are a powerful identification tool, but they aren't failsafe. Here are some of the drawbacks:

• The microchip may migrate away from its intended location. A small capsule of scar tissue usually develops around the microchip and keeps it in place. But occasionally a microchip can come loose from its moorings and migrate to a new spot. This is harmless to the cat, but can make the device harder, or even impossible to detect. It's a good idea to periodically have your veterinarian check that the microchip is in its proper place and in good working order.
• The microchip is not a visible form of ID. The microchip will not help a well-meaning neighbor identify your cat when he shows up on their doorstep. The cat must be taken to a veterinarian or an animal shelter that has the proper scanner to decode the hidden message. All microchipped cats should still wear a visible ID collar or tag as backup if possible. The collar or tag should have owner contact information and/or the microchip ID number.
• Microchips have been associated with tumors in laboratory mice. This has been documented in research animals, where microchip technology is widely used. It can raise particular concern among feline owners, who may be aware of the well-documented association of certain vaccines and an aggressive form of cancer in cats known as fibrosarcoma. A few anecdotal reports have described such tumors arising near the implanted device in feline patients. However, larger studies fail to show an increased risk. Experts point to the fact that the incidence of fibrosarcoma in cats has not risen along with the growing use of microchips use the way it did with certain vaccines two decades ago. Depending on your cat's lifestyle, the risk of cancer may be far outweighed by the chance she will get lost over her lifetime. Your veterinarian is best qualified to help you make the call.
• Infection and bleeding at the injection site are two possible, but uncommon complications. Be sure to notify your veterinarian if any swelling, tenderness, or discharge develops in the area where the chip was implanted.
• Standards and cross-compatibility are still emerging. Incompatibility issues remain a major pitfall for microchips in the United States. That is, some chips justaren't readable by some scanners. This is despite the introduction of a so-called "universal scanner" in 2006. Competing microchip companies have resisted the push towards a universal standard, and North American chips and scanners typically fail to comply with accepted protocols worldwide. Today, most animal shelters employ two or more types of scanners to avoid a potentially tragic oversight. And although microchip manufacturers readily supply readers to animal shelters for free, there are no regulations in place to ensure they are used. There are still those unfortunate few cases where microchipped pets have fallen through the cracks.

Stay tuned. As compatibility issues are resolved and new laws are enacted, microchip technology for cats is here to stay. For advice about microchips, including which, if any, chip format predominates in your area, it's always best to consult your veterinarian.