Garmin’s D2 series of aviator watches give pilots a powerful alternative to smartwatches from Apple, Samsung, and other manufacturers. The newest version, the D2 Delta PX, adds a useful new feature that pilots will love, a built-in pulse oximeter (hence “PX”) for measuring blood oxygen saturation levels. The D2 PX is the largest of the series, with a case size of 51 mm, and also the most expensive at $1,249. D2 Deltas are also available in 42- and 47-mm case sizes, but don’t include the PX sensor.

The D2 Delta is a standalone replacement for digital smartwatches because it can handle those devices’ chief function—notifications—while adding a bunch of aviation-specific features that aren’t available on other watches. Surprisingly, development of aviation features hasn’t taken off with smartwatches, leaving Garmin’s D2 aviator watches as among the few choices for pilots who like aviation information on their wrists.

Because the D2 series watches are based on Garmin’s Fenix multisport watch, the D2 offers a full range of sporting activity functions as well as wrist-based heart rate, activity profiles, and fitness tracking. The watch also features Garmin Pay, it’s contactless payment system, and can store up to 500 songs that can be played via Bluetooth-connected earphones. Battery life is amazingly lengthy, at up to 20 days in smartwatch mode or 18 hours in GPS mode.

Garmin has greatly improved the watch band attachment system on the D2, with QuickFit bands. These are simple to remove, with no need to disconnect pins, just push back a latch and the band comes off. Bands are available in leather, metal, or silicone.

The bezel is made of black titanium married to a fiber-reinforced polymer case with a sapphire crystal. The display measures 1.2 inches and has 240 x 240 pixel resolution. The D2’s water rating is 10 atmospheres, which means the watch is safe to a depth of 100 meters.

In a relatively small package, Garmin has stuffed a lot of sensor technology. The D2’s positioning sensors include GPS, Glonass, and Galileo. The watch measures heart rate in addition to oxygen saturation. A baro altimeter with settable alarms could be helpful during a pressurization emergency. Other sensors include a gyroscope, accelerometer, compass, and thermometer. The watch automatically logs flights.

There is so much that this watch does, it’s almost a bit intimidating at first. The watch has five buttons on the case, and it’s important to learn and understand what each one does before randomly pushing buttons and trying to figure out how to get to a specific function. It does take a while to get comfortable with the D2’s various menus and settings, and it is well worth spending time with the manual before taking it flying or adventuring.

The easiest way to start using the D2 is to plan a flight and figure out how it can fit into your planning process.

Before doing anything with the watch, its databases need to be up to date. Powering on the watch launches a screen with the latest database info, and if it isn’t current, plug the watch into your computer to update it using the flyGarmin app. You’ll also have to install the Garmin Connect app on your smartphone to take advantage of notifications and sharing features.

Once updated, to check the weather at a nearby airport, press and hold the back button to find the nearest airport. (Note that many functions rely on a GPS signal, so it might be necessary to do this near a window or outside.)

Selecting nearest airports brings up a list of airports including their distance and bearing, a useful emergency feature. Pressing the Direct-to button pulls up a menu, starting with direct-to for navigation to the airport, then airport information and weather, including Nexrad. Current weather and Nexrad requires internet via connection to a smart device paired to the watch. If not connected, the watch will still show the Metar and TAF, but these will be the latest to be downloaded, not the most current information.

You can add “widgets” to the widget loop, which is accessed by pushing the down button. Using the Metar function in the widget loop, it’s easy to enter an airport ID to get the weather for that airport.

Time To Fly

When it’s nearly time to fly, you can add a flight plan either by transferring it from Garmin Pilot or by entering it using the watch buttons. This takes a little longer because you have to select each letter or number from an alphanumerical list.

The navigation features are some of the most interesting in the Garmin watches and could come in very handy in the event of loss of navigation capability in the airplane. The watch can also act as a position sensor for Garmin Pilot when running on devices that don’t contain a GPS receiver.

The navigation database is worldwide, so the watch is useful anywhere. Direct-to is the easiest way to navigate to a waypoint, either by keying in the waypoint or selecting from a nearest list. It is also possible to use the “Finding a Waypoint” function either to search for a waypoint by name or select from a list of nearest airports, navaids, or intersections.

Once navigating, cycling through the widget loop serves up a bunch of information. There is an HSI display that looks like a real HSI. Various instruments, which are customizable, are displayed such as baro altitude, groundspeed, track, and vertical speed, nearest airport information and desired track, ETE, and distance to the selected waypoint. If connected to air data from the airplane via a Garmin Flight Stream wireless gateway device, the watch can also display air data, including indicated airspeed, true airspeed, outside air and total air temperature, pressure and density altitude, and more.

One of the watch’s handiest features is the fuel tank reminder. This is customizable; I have it set on 30 minutes, and at the specified time, it vibrates on my wrist in a Morse code pattern of dots and dashes. These vibration patterns are selectable, too, and there are five choices: S, D, R, G, or O. I like “O” with its three dashes because the dashes last longer and are easier to feel on my wrist.

The pulse oximeter alone might be enough to make the watch worthwhile. U.S. Navy pilots have been using Garmin Fenix 3 watches for a few years, but to help determine cabin altitude. They might like the D2 PX better because of the pulse oximeter, which adds more information than just the baro altitude inside the aircraft.

It would be interesting to take the D2 PX along on an altitude chamber ride to see how it compares to a high-end pulse oximeter. And it would be helpful to determine the altitude and pulse oximeter reading (SpO2) on the watch at which the wearer starts to experience the effects of hypoxia. It should be noted, however, that Garmin warns that this watch is not a medical device and shouldn't be used to diagnose any condition. In any case, pilots must adhere to regulations concerning when they must use supplemental oxygen.

For my testing, I wore the watch during airline and business jet flights and compared its readings to a low-cost Clinical Guardian pulse oximeter, the kind that clamps onto a finger. It’s important to hold fairly still to get an accurate SpO2 reading from the watch.

Generally, the watch was more pessimistic than the finger pulse oximeter, so the watch thus provides more margin of safety.

For example, at 7,300 feet cabin altitude in a Boeing 737, the watch read 84 and the pulse oximeter 90 percent. In a Hawker 800 at 2,800 feet cabin altitude, the watch read 86 and the pulse oximeter 95. Then at 2,100 feet, the watch gave a reading of 84 and the pulse oximeter 93 percent. But both had closer readings in other cases; in the Hawker at 2,000 feet cabin altitude, both read 92 percent and at 5,600 feet both read 91 percent. Another reading in a 737 at 7,000 feet cabin altitude saw the watch with 94 and the oximeter with 93 percent.

I don’t think I was feeling any effects of hypoxia at the lower readings, but if I saw those oxygen saturation levels while flying, I hope I would try to get to a lower cabin altitude.

I tested the watch on a healthy subject who teaches at a local gym, and her resting SpO2 was 99 percent; the same number displayed on the Clinical Guardian pulse oximeter.

The watch records pulse oximeter readings and also the cabin altitude and then plots both on a widget screen so you can see how the saturation has changed relative to elevation over the last 24 hours. While flying, the watch logs saturation levels more frequently. There is also a separate SpO2 gauge—available when in Fly mode—that shows the individual reading along with color bands for a quick and easily viewed indication of the level (red, yellow, green).

Overall, the Garmin D2 watches cram a ton of technology and features into a wearable package that provides a lot of information and suitable backup for emergencies. The PX’s pulse oximeter, while bumping up the watch’s price fairly significantly, makes it all the more worthwhile. If there is a drawback to the D2 watches, it is that they are complex, and it’s essential to spend time learning how to use them before trying to figure it out while at the controls of an aircraft.