My cat lives full time in my flat and doesn't go out onto the street.  But as a result of an attempted break-in, she escaped and went missing.
I couldn't leave the house to go and find her because I had to deal with the police and maintenance people, but I did not need to!  I remembered that when I had adopted her 12 years ago she had a MicroChip and I still had the tag.
I called PETtrac and they registered the chip - even though it was from the US - and sent me out a registration form.
A few hours later - to my surprise and delight - I got a call from a local vet.  Nearby neighbours had found my cat and taken her to the vet as a stray.  The vet had scanned her chip, got onto PETtrac, and they got onto me.
We were reunited within a day - I couldn't have asked for a better or quicker outcome!