ID tag vs. microchip: why you should have both.

A microchip is the answer if your pet is found by a vet or shelter. It's not the answer if your pet is found by a neighbor.

A tag is the answer for the neighbor. It's not the answer if the tag ever comes off, or gets so scratched the number can't be read.

One works when you're not there. The other works when a vet is. They aren't alternatives — they're teammates.