It contains a radio transmitter, an antenna, and a computer chip with a 15-digit code (ISO chips). The information contained in a microchip has to be read by a scanner -- it is not a GPS system that will allow you to track and locate your pet.
The more worrying concerns are the admittedly rare medical complications that a microchip implant can cause. In 2009 there was the case of a Chihuahua hemorrhaging to death in California due to mystery bleeding put down to the microchip implant. There have also been complications when the chips have been implanted into the wrong area of the animal — something highly unlikely with a qualified veterinarian — or when the chip has migrated within the animal’s body. These have usually been harmless but can sometimes cause infections or abscesses. Finally, there have been reported cases of tumors developing in and around the area in which the implant was made, though this in itself does not necessarily mean it was due to the implant itself.
Furthermore, There have been two documented cases in veterinary medicine where sarcoma or fibrosarcoma, two types of soft tissue tumors, occurred at the site of the injection. While two cases are not very many, I believe there are likely many more cases that have not been documented. Research shows that between 1996 and 2006, up to 10 percent of laboratory animals had some type of reaction to being microchipped, ranging from a localized inflammatory response to tumor formation at the site of the injection. Needless to say, it’s important to realize that implanting any foreign material into your pet’s body is a risk.
So if your pet has been microchipped, make sure you have a vet scan to identify exactly where it is. Once you know where it is, check it once a month to make sure there are no changes, at that it doesn’t feel any different.
If you can feel your pet’s microchip, it will feel like a grain of rice under your pet’s skin.
After all, the above procedure is mandatory for all pets travelling in to EU countries and so many other countries. So there are no alternative methods.