We have 6 cats, and they are all chipped. 4 are in/out; 2 are in only.

Doesn't take any time at all to chip them; every Vet visit they check to make sure it is still there. Couple of years ago we took a stay to our local Humane Society - first thing they did was check for a chip.

A cat or dog can lose a collar, but the chip stays.