Pet chips.

Forget doggy tags! The coolest cats in Hawaii are sporting microchip IDs.

Veterinarians (animal doctors) inject these tiny computer chips under a cat's skin using a hypodermic needle. Each chip has been preprogrammed with a unique ID number, which the chip broadcasts as a radio wave signal.

To trace a cat back to its owner, a veterinarian simply sweeps a radiowave scanner over the animal's back. If the cat has an ID chip, the ID number pops up on the scanner's screen. A computer matches the number with the animal's home address.

Why use such a hightech cat-tracking method? Hawaiians are trying to keep tabs on cats that have owners so they don't confuse them with the estimated 90,000 to 100,000 strays.

Stray cats often carry diseases. They also kill song birds and small mammals, many of which have become extinct. stray cats are often euthanized -- humanely killed.

The problem of strays is not unique to Hawaii. Some Australians recently proposed eradicating all cats from their continent by purposely spreading fatal feline diseases in the wild.

But Rebecca Rhodes of the Hawaiian Humane Society says the problem of strays would be solved if people had their cats spayed or neutered, so they couldn't reproduce, and didn't let them roam free for days at a time.

And if a cat has an ID, it can be safely returned to its owner, instead of losing the last of its nine lives.