Oscar, the dog, came with a chip, I have no idea if our vet has checked it or not.
He and the cats also have tattoos. Sophie's tattoo brought her home to us when she was hit by a car. She survived the car accident.
I have not looked into having the cats chipped. I would consider it if we traveling away from home with them. Sophie does go camping with us, but only with in 3 hours of home.
I did recently hear of one dog where the chip had moved and the vet had to scan the lower leg to pick up the signal.