When several people recently tried to claim a lost golden retriever at the Contra Costa County animal shelter, it was a microchip embedded in the beautiful-and sought-after-dog's shoulder that proved the true identity of its owner.

"It's the only unalterable method of claiming your pet," says Julie Cummings, DVM, with Lafayette's Four Seasons Animal Hospital and president of the Contra Costa Veterinary Medical Association. "Tags and collars can be removed."

Since July 1, the Contra Costa County animal shelter has been scanning each lost cat and dog that comes through its doors, looking for an invisible identification number telling them the name of the rightful owner. The practice has reportedly been useful in reducing the number of unclaimed animals put to sleep.

Makers of the chips say once injected, the device, which registers an ID number unique to your pet and is small enough to pass through a hypodermic needle, stays put in the shoulder tissue of an animal for life without causing allergic reactions. Handheld scanners then use radio signals to read the number through your pet's skin, allowing shelters to let you know they have your lost loved one safe and sound.

Dogs and cats who repeatedly break loose from home are good candidates for microchipping, as are pets who refuse to wear collared ID tags. However, even indoor animals should be considered for microchipping because it only takes one open door or gate to lose a pet forever.

Costs can range from about $20 to $40, and there is an additional cost for registering your pet's ID number with the tracking agency the shelter calls after identifying your pet. You can even provide the tracking service with a friend or relative to contact if you're out of town or unavailable.

But, says Cummings, who performs about five microchip injections each month, it should never completely replace a tag with your name and number hanging from your pet's collar. ARF now microchips each of its animals prior to adoption. If your ARF cat or dog gets lost, ARF will be notified and will contact you. Or, you may choose to add your name to the registration so that you will be notified directly. Either way, your pet has a much greater chance of being returned to you safely and quickly. To learn more about microchipping, contact ARF at (925) 256-1ARF or call your local vet.