There is plenty to consider when buying a smart ring, so use these tips to help you narrow your choice and get the best from it.

Size: Some smart rings come in standard sizes, but there is some variation, and half sizes are rare. Most manufacturers will send you a free sizing kit, enabling you to wear a dummy ring for 24 hours to ensure you get the right fit. (You may have to buy the ring directly from the manufacturer to get this kit for free.) You should absolutely do this. Bear in mind that your fingers swell and shrink over the day. Your smart ring should be snug to enable the sensors to measure accurately, and it will work best on your index finger (though the middle or ring finger can work).

Finish: All the smart rings we tested combined tough titanium with a sensor array on the inside, but the coatings and colors vary. If you are hard on rings, a silver or gold finish will likely suit you best, as there is less risk of damage. My Oura and Ultrahuman rings with black finishes have visible scratches and chips after a few months. The Oura and Amazfit rings have tiny dimples to help you align the sensors. While I prefer the smooth finish of the Ultrahuman, I suspect correct placement aids accuracy enormously.

Care: If you want to avoid damage, you should remove your ring when working with tools, weight lifting, washing pots and pans, or even cleaning the sink. If your ring is likely to rub against a surface, take it off. I found this was a bigger problem wearing a ring on my index finger than with the middle or ring finger. I scratched the Oura and Ultrahuman rings when gardening, moving boxes, and using a dumbbell. Titanium is also tough enough to damage surfaces in your home. I gouged the porcelain of my sink and marked the inside of a mug with the angular Ringconn. All the smart rings we tested are water resistant, so you can swim or shower without taking them off.

Charging: Smart rings come with a charger and cable, but you will generally have to provide your own wall adapter. From dead, they take anywhere from an hour and a half to three hours to fully charge, but you should avoid letting the battery run down completely, or you run the risk of losing data. We tested the smart rings above with all the bells and whistles turned on, so our battery life estimates are lower than the manufacturers claim.

Features: Most smart rings will track your sleep, heart rate, and temperature. If you want to keep an eye on your sleep and health unobtrusively and comfortably, smart rings are ideal. Fitness tracking varies, with most smart rings offering basic step counts and movement, some offering manual workout tracking, and only the Oura and Galaxy Ring offering automatic workout recognition. But you can expect more depth and accuracy from a traditional fitness tracker or smartwatch. Combining a smart ring with an Apple Watch or Fitbit makes for a seamless experience, allowing you to take off the watch and let it charge at night without gaps in your tracking.