Like many other users, my CT10s stopped working very soon - 3 of them failed on the first round, and at least 2 failed every single round after that. Garmin will tell you it might be the battery (it isn’t, unless new batteries drain within days), and they will tell you that many other people use these sensors and don’t have any problems (ignore the other forum posts stating otherwise).
Finally, they’ll tell you you’re outside the 30-day return period so they aren’t eligible for a refund. If you are thinking of buying these sensors, save your money, and consider alternatives.