The Fi collar is lightweight and can comfortably fit dogs 10lbs or more, with neck circumferences' of 11.5" and up.
While we don't have an extra small size developed at the moment, we hope to have one at some point in the future!
Since we've designed and tested Fi specifically for dogs, our product isn't optimized for cats or pets other than dogs.
We do not recommend using Fi to track your cat, as we don't expect a comfortable fit or optimal performance.