A bit of info I found out -- just because a pet is microchipped, it doesn't mean that the information it needs to get home is associated with the chip. The chip only gives a number when you scan it. The pet owner needs to register the number to associate it with contact information. There are many people who have microchipped their pet and never bothered to register. In that case the chip is totally useless.

Also, there is very little security with chip registration. If someone has your pet's ID number, that person can register it and claim your pet as their own. I'm surprised by the lack of security in this system.

Finally, make sure you have an ISO-compliant microchip. In some countries they cannot read non-ISO-compliant chips.