Quick answer: The best smart collar for cats is lightweight (under 30g total), has a long battery life, offers location tracking, and includes a safety breakaway mechanism.
Cats are much more sensitive to collar weight than dogs. A tracker that adds more than 15-20g to the collar causes stress, fur damage, or will be removed by the cat. Look specifically for trackers designed for cats — don't adapt dog trackers.
For cats, GPS location tracking is far more valuable than activity monitoring. Cat activity is naturally erratic and harder to interpret meaningfully. Focus your budget on tracking accuracy and battery life rather than health features that provide less actionable data for cats.
Any collar on a cat should have a breakaway or safety release mechanism so the cat can free itself if caught on a branch or fence. Some GPS collar designs eliminate the breakaway for a more secure fit — this is dangerous for outdoor cats. Never compromise on safety release.
For cats, a lightweight GPS tracker on a safety breakaway collar outperforms a full smart collar in both safety and utility. Prioritize safety release, weight, and tracking accuracy.