After three years, GARMIN finally made a major splash in the dive market at the end of 2023 with the launch of the Descent Mk3i and the Descent T2 transmitter. Together, these two products leverage GARMIN's proprietary SubWave sonar technology to elevate dive safety and underwater usability to an entirely new level. If you want to learn about the Descent Mk3i launch details, check out this article: GARMIN Dive Computer Launch Event — Mk3's New Flashlight and Underwater Messaging? We Unboxed It Straight Underwater.
The Garmin Descent Mk3i and Descent T2 transmitter finally opened up underwater text messaging in 2024.
Before You Start, Update Your GARMIN Mk3i and T2 Transmitter
If you were an early adopter and picked up the GARMIN Mk3i and T2 transmitter at the end of 2023, the firmware at that time had not yet been updated to support underwater text communication. Before using the underwater messaging feature, please connect your devices to the GARMIN Connect app on your phone and perform a firmware update.
Firmware versions required for underwater communication support:
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Mk3i must be updated to v15.62 or above
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T2 must be updated to v2.23 or above
Connecting to the T2 via the GARMIN Connect app
You might assume that the T2 transmitter needs to be attached to a scuba tank / cylinder to power on, but in fact, simply removing and reinserting the battery will briefly trigger the T2 to activate for pairing — very convenient. The connection process with your phone is smooth and straightforward; just follow the step-by-step instructions in the GARMIN Connect app.
Once your phone finds the T2, the app will guide you through the firmware update.
After completing the firmware update, you can proceed to pair the T2 with your watch. Don't forget to give your transmitter a memorable and cool name! Also, since a single GARMIN Mk3i can be paired with up to 8 T2 units, the initial setup will take a little time as you pair them one by one. Once pairing is complete, you're ready to dive!
After pairing, you can see the tank pressure (SPG) and depth of your dive buddies.
Bonus: How to Install the T2 Transmitter Extension Hose
Some first stage regulators have narrower high-pressure port openings, making it impossible to mount the T2 transmitter directly. In that case, you'll need to add a high-pressure extension hose to connect the T2 to the first stage regulator. Note: you cannot simply attach the T2 directly onto the hose — a small modification is required!
Step 1: Remove the spindle from the T2 transmitter. Use a flathead screwdriver and do it slowly and gently.
Removing the high-pressure spindle from the T2 transmitter
This is what it looks like once removed.
Step 2: Install the high-pressure hose spindle included with GARMIN. Pay attention to the orientation — the tan-coloured O-ring should face toward the high-pressure hose.
Mind the installation direction — the tan-coloured O-ring faces toward the high-pressure hose.
So what revolutionary changes does the combination of GARMIN Mk3i and T2 transmitter bring to the diving experience? Before we get to that, let's take a look at the hardware and software upgrades that make the GARMIN Mk3i stand out.
Upgrade 1: Refined Interface — Near-Perfect Typography
The Garmin Mk3i features a significantly improved interface.
The common feedback from Garmin Mk2 users was that the font was too small and the screen too cluttered with information, requiring constant display switching just to find what you needed. The Garmin Mk3i addresses this in a big way — fonts are larger, and when switching between display views, essential dive data remains visible on screen at all times, eliminating the need to constantly cycle through screens underwater.
Additionally, the Garmin Mk3i's display brightness is in a completely different league from the Garmin Mk2, making it far easier to read critical information at a glance during a dive.
Upgrade 2: Emergency Lighting — Backup Flash Light
When your Flash Light dies, you can activate the emergency backup light on your watch.
Most divers have experienced their Flash Light dying during a night dive. If you happen to be carrying only one light, that's a genuinely scary situation. The GARMIN Mk3i addresses this by adding an emergency light source at the top of the watch, giving you a backup to safely return to the surface in an emergency.
This light isn't as powerful as a dedicated Flash Light, but real-world night diving tests confirm it's more than adequate as an emergency backup. This feature reflects how GARMIN develops products by extending functionality based on users' actual needs.
Upgrade 3: Dive Readiness Score — Raising the Bar on Dive Safety
The GARMIN Mk3i introduces a Dive Readiness Score so you can fully assess whether you're fit to dive on any given day.
GARMIN has long offered a range of health-monitoring metrics — including heart rate, sleep quality, and body fatigue — to help you better understand your physical condition. With the Mk3i, GARMIN integrates all of these data points into a "Dive Readiness Score," a quantified indicator that tells you whether you should exercise extra caution before diving on any given day to reduce risk. This score does not directly adjust your watch's conservatism settings or NDL; it's purely a reference tool. You still need to make the final call on whether to dive based on how you're actually feeling.
The GARMIN Mk3i analyses your personal health data to recommend your Dive Readiness Score for the day.
This feature is especially helpful for those of us who frequently travel abroad to dive. For example, if you've just arrived on a red-eye flight without adequate sleep, or you've had an exhausting travel day and feel okay on the surface but your body hasn't fully recovered — this score gives you a rough indication of whether you're truly ready to dive, or whether you should maintain a heightened level of safety awareness underwater.
Are Underwater Messaging and Tank Pressure Monitoring Actually Useful?
Before reading the breakdown below, here's the bottom line: They are incredibly useful!!! Let us share why the Editor thinks so, from several angles and real-world use cases.
Underwater research teams highly recommend the GARMIN Mk3i and T2 transmitter for safer underwater operations.
Top Reason #1: Tank Pressure Monitoring Keeps You on Top of Your Buddy's Status
The watch displays your paired dive buddy's depth and tank pressure (SPG).
With the GARMIN Mk3i paired to up to 8 T2 transmitters, you have complete visibility of the tank pressure for every dive buddy around you. This is an incredibly practical feature for dive instructors and dive guides, as it eliminates the need to check in with each diver individually — all the information is right there on your wrist at a glance.
Top Reason #2: Knowing Your Buddy's Depth Makes It Much Easier to Find a Separated Diver
You may have noticed that in addition to tank pressure, the display also shows the current depth of each paired diver. This might not seem like a big deal at first, but the Editor found it to be a genuinely impressive feature in practice. During a dive trip to Bohol in the Philippines — a year when visibility happened to be particularly poor — the buddy depth function, combined with directional navigation and the transmitter's range limitations, proved to be a reliable way to locate dive buddies who had drifted away while taking photos.
A real example: We were doing a wall dive with the wall on our left. The GARMIN Mk3i showed a buddy at 15 m, so we descended to that depth. When the signal began to weaken and eventually drop out as we moved in one direction, it was a clear indication the buddy was actually in the opposite direction — dramatically improving the odds of a successful reunion.
Top Reason #3: "Are You OK?" and "Come Find Me!"
Underwater text messaging is the biggest highlight of the GARMIN Mk3i update.
Everyone knows that hand signals are essential underwater, but when your dive buddy is too far away to see — or has gone missing — the GARMIN Mk3i's built-in text messaging feature comes into its own. In our real-world tests, a sent message was received by nearby dive buddies within approximately 3–5 seconds. According to GARMIN's official specifications, the effective range for text messaging is approximately 5 m. The Editor plans to use a measuring line on a future dive to test just how far the effective transmission distance actually reaches.
While this feature is genuinely useful, there is one notable limitation: the GARMIN Mk3i currently only supports a set of pre-written "canned" messages and does not allow custom text input. The selection of pre-set messages is also fairly limited. We hope GARMIN will expand the canned message library over time and eventually develop a custom message input feature, so that underwater text communication can truly reach its full potential.
GARMIN Descent Mk3i — Final Verdict
Underwater text messaging significantly enhances dive safety.
The combination of the GARMIN Descent Mk3i and the Descent T2 transmitter introduces an entirely new workflow and set of use cases to diving. Not only does it bring genuine technology into the dive experience, it also substantially raises the safety bar underwater. We look forward to seeing GARMIN continue to push the boundaries with new innovations that reshape what we thought was possible in diving. Of course, if we had to name one downside, it's that the budget for the GARMIN Descent Mk3i paired with the Descent T2 falls firmly in the mid-to-high-end range — so get ready to lighten your wallet if you want to experience this exciting new feature!
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