The use of a microchip allows your pet's ID number to be stored just under the skin, where it cannot be lost, altered, or worn and unreadable like an external tag. A microchip can greatly increase the chance of recovery should your pet become lost.
A microchip is a tiny, totally inert electronic transponder about the size of a grain of rice. The chip is implanted into an animal using a simple, painless procedure similar to a routine vaccination. For most animals, the chip is implanted in the scruff of the neck. The procedure takes seconds and does not require anesthesia. After implantation, the device remains with the animal for life.
Once implanted into the animal, the microchip remains inactive until read with a scanner. Scanners send a low fequency radio signal to the chip, providing the power needed by the micoship to send its unique code back to the scanner with the animal's ID number.
The City of Folsom offers microchip service for $20. Contact the City of Folsom at 355-7230 for more information.
Taken from Microchip Identification by Bob Christiansen