Microchip
A microchip is a small grain of rice sized passive electronic circuit that requires no maintenance and is placed under the skin between the shoulder blades with a hypodermic needle and is used to identify your pet.
Animal shelters, veterinarians and other animal care facilities have “scanners” that can read the unique serial number in the microchip and then check a database to find the owners registered information. Microchips are not a GPS device. How it works
Microchips used in the United States differ from those that are used in Europe. Therefore folks that are planning travel to Europe with their pets should have both the U.S. chip and the European (ISO*) chip in their pet.
Fortunately Fondren Pet Care Center carries both the U.S. and ISO chips and has scanners that read both.

* International Organization for Standardization 11784/11785