My cats are not chipped, but my dogs are. The dogs are much more likely to be "lost" than the cats, if they get out of the yard (yes, I'm saying the cats are much better at staying at home! LOL!!)
Our chips are through AVID. The veterinarian keeps a log of every animal he chips and turns it into AVID. That number matches up with me, so if Honey and Lilly are ever lost, if the rescue or veterinarian they are taken to has access to a scanner, they will know this dog belongs to someone. Even if it is not an AVID scanner it does pick up on the chip.

The chip itself is about the size of a grain of rice. The veterianarian inserts it with a syringe of sorts right between their shoulder blades (same for cats and dogs). It has little "teeth" that prevent it from moving around, but I always have my vet check for it when we're in there, just to make sure that it is still reading their number.

My dogs also have an extra tag on their collar signifying that they are chipped. You just have to be sure to let AVID know if your address or phone number changes. You want them to be able to find you.

There is a wide range of cost for this service. It was $50/dog for me to do it. But I have heard as low as $15. So check around and get the best price.

Logan