Don’t let your pet become one of the 10 million dogs and cats lost each year. A tracker lets you know exactly where your pet is, even if somehow it has crossed the country. GPS units that attach to your pet’s collar transmit coordinates to your phone, letting you know where your pet is in real time—and where it has been, which will help you figure out how it got there. Some units also function as fitness trackers, and many (but not all) require subscriptions, which means you’ll have to pay a small monthly fee. Here’s a guide to choosing the best pet tracker for your best friend.