How do I check if a microchip already has a registered owner

How do I check if a microchip already has a registered owner?

Enter the microchip number in the Microchip Lookup tool at the top of petlink.net — if the chip is registered, the pet's name and owner details will appear.

If nothing comes back, the chip is not registered with PetLink and can be registered at https://www.petlink.net/account/register-pet/