Here are some features I genuinely never thought I’d see on a watch: subaquatic topo maps; a dive-readiness tracker; underwater text messaging. Shockingly, all of these features exist on the Garmin Descent Mk3i, the most lusted-after top-of-the-line smartwatch and dive computer on the market. After two months of using the Mk3i for running, hiking, and diving, I can confidently say it’s the only watch I’ll ever need for the foreseeable future, and, apart from the significant pricetag hurdle, a no-brainer for anyone who spends time underwater.

　　How Is It as a Regular Smartwatch? I’ve found that most dive watches that also profess to work as daily smartwatches are not worth the cost. There are almost always tradeoffs, like poor app integration, bulky or technical looks, and hard-to-read screens, especially underwater. (Luxury “dive watches” are not helpful for fitness on land or underwater).

　　The Mk3i has the same operating system and features as Garmin’s high-end smartwatches, like Outside favorite Fenix 7X, or the extra-fancy epix Pro. It has outstanding GPS accuracy and comes with preloaded maps, excellent fitness tracking, painless integration with third-party apps like Spotify, and easy-to-navigate menus. Importantly, it also looks sleek: apart from the larger, 51-millimeter face, the Mk3i wouldn’t look out-of-place at an upscale restaurant.

　　Welcome to the Future As a basic dive computer, it does everything exceptionally well. Its Bühlmann ZHL-16C decompression algorithm works as it should. Air integration (in the “i” models) using Garmin’s new T2 transceiver never skipped a beat or lost connection. Setting bearings and navigating underwater are easy with the compass. Critically, screen brightness and sharpness are next-level. The Mk3i has a 454454 pixel AMOLED color touch-screen display, an upgrade from the Mk2, which had a light-reflecting MIPS display. Even for a far-sighted person, I had no trouble reading my watch sitting on a dive boat in midday sun.

　　Now to the James Bond stuff. Yes, you can send messages underwater. Six basic preloaded messages (“Are you okay?,” “Come to me,” etc.) travel via “Subwave” sonar to anyone else using a T2 transceiver. I didn’t have the chance to test it out since my dive partner was using an older Mk2 and T1 transceiver, but fellow divers tell me it works as advertised. It seems mostly helpful in low-visibility scenarios where hand signals are impossible, but for regular dive buddies who invest in the equipment, it’s a very cool perk.

　　Despite the inability to message my partner, I was still able to see his tank pressure, distance, and depth on my watch, which meant I never had to worry if he was running low on air or drifting too far away. The ability to track up to eight different transceivers is a game-changer for dive instructors with big groups.

　　Other futuristic features? DiveView Maps, a highly detailed topographic underwater map that lets you see exactly where you’re jumping in (it doesn’t track you below the surface, unfortunately). A “readiness score,” similar to a training recovery score on other tracking devices, judges your alertness and physical health for diving based on how well you’ve been sleeping, heart rate, jet lag, and other indicators. This was, however, the only Mk3i perk I found superfluous. If I refused to dive after every red-eye, I’d never dive at all. Lastly, the watch has a super bright flashlight that I initially thought was a bit gimmicky, but proved very useful for peering into dark nooks and crannies for octopuses and other reclusive creatures.

　　The most miraculous thing about the Mk3i is its battery life. Garmin claims up to 66 hours in Dive Mode. I spent three full days diving in Cozumel, Mexico and another day cave diving in cenotes outside of Mérida, and still had 89 percent battery life. For reference, the Mk2 had roughly half that battery life, and some competitors can hardly make it through a day of diving. If you took the Mk3i on a two week-long liveaboard and forgot your charger, you’d probably last the entire trip.

　　The High Price of Perfection Predictably, the Mk3i has one major downside: price. At $1,600 for the 51mm version (or $2,100 if you need a new transceiver), this is one of the most expensive smartwatches Garmin makes. It’s far too expensive for someone who only goes diving once or twice a year. If you need a top-end fitness-tracking watch and you’re a regular diver, however, the exceptional performance in both use cases makes it a reasonable splurge.

　　Need a great smartwatch and only dip your toe in the water? The Apple Ultra 2 ($800) offers a very basic dive computer via the Oceanic+ app. And, if you just need a simple, reliable dive computer separate from your watch or fitness tracker, a $230 Cressi Leonardo will do the job—just don’t wear it to dinner.