Project Description

Making Sense out of Swim Data
What would happen if you tried to take your favorite fitness device for a swim? Angry fizzing as the innards collide with water? While the market for connected fitness devices has become more diverse, expanding in functionality to track all kinds of metrics for all kinds of sports, there’s a problem—not all sports take place on land.

What if, like me, you were raised as if you had fins instead of feet? Or what if, also like me, you sustained an injury that precluded you from most land sports (at least for the time being)? If you’re anything like me, you are desperately seeking a fitness device that’s not afraid to get wet—a device that delivers meaningful data, in a meaningful way, to swimmers.

I harnessed my inner Michael Phelps mojo and put two dedicated swim monitors—the FINIS Swimsense Swimming Performance Monitor and the Garmin Swim—to the test. How did the two fitness watches stack up? In the sport of swimming, winning is often in the details—the starts, turns, finishes, and streamlines off the wall. In the battle of the connected swimming devices, it came down to the technology details.

Accurate Accelerometers
Having grown up in the desert, I have been swimming for as long as I have been walking. I was one of many young Arizonans who spent countless summer days at the pool, waking up at the crack of dawn to swim laps with my team, building strength and honing skills for years of competitions to come.

While I am not a new swimmer, I imagine there are plenty of newbies looking to pick up the sport after the residual excitement from the 2012 London Olympic Games. Whether you are looking to compete on a local team, or simply to unwind after a hectic work day, a connected device may be the tool you need to make sense of your next swim.

In fact, “Make Sense of Your Swim” is the tagline for the FINIS Swimsense Swimming Performance Monitor ($199.99), which I pitted against the Garmin Swim ($149.99) in my hands-on product test. The two devices offer up similar realtime data: lap counts, total distance swum, elapsed time, calories burned, and more. Both solutions also offer an online Web portal to track workouts, similar to other industry-leading fitness watches for land sports, with the added twist of calculating a “SWOLF” efficiency score, which combines the time and number of strokes it took to complete a lap (lower scores are better, like in golf). The name, if you’re curious, simply combines the words “swim” and “golf,” thus illustrating the lower-score-is-better approach.

What distinguishes these aquatic devices from their land counterparts, besides submergibility, is their ability to decipher, via embedded motion-sensing technology, which stroke you’re swimming. Using computing programs and algorithms, the onboard sensors can determine freestyle from backstroke from breaststroke from butterfly with uncanny accuracy. Both companies seem to have honed in their algorithms, because I couldn’t seem to fool either device. If, for instance, I swam “sidestroke,” corkscrew (one stroke freestyle, one stroke backstroke), or some other made-up stroke, the devices would simply label the interval “Mixed Stroke” (on the FINIS Swimsense) or “Mixed” (on the Garmin Swim). Even my husband, who was wearing the FINIS device during his first attempt at swimming butterfly, received an accurate label once we uploaded his workout, meaning your stroke doesn’t need to be perfect for the algorithms to understand what you’re doing.

Unlike fitness monitors built to calculate distance via GPS, these swim monitors rely on accelerometers—electromechanical devices that measure dynamic acceleration in the form of your movement through the water. Both devices’ accelerometers are calibrated to pick up the stop/start motion between individual laps. For this reason, the devices are only helpful when swimming in a pool. If you are an open-water swimmer who prefers swimming in lakes and oceans, FINIS offers an alternative—the Hydro Tracker GPS ($129.99), which attaches to your goggle straps and tracks your swims via GPS. Garmin also offers the Forerunner 910XT ($449.99), a GPS-enabled multisport device that can provide metrics for open water and pool swimming, along with running and biking data on land.

The FINIS Swimsense also has onboard magnetometers, which work with the accelerometers to determine subtle changes in your direction and motion. Magnetometers are among the sensors commonly found in smartphones to help determine a device’s three-dimensional orientation. Luane Rowe—Australian swimmer, open-water champ, and industrial designer at FINIS—tells me the magnetometer data helps calculate the stroke type and the accelerometer data helps calculate when you start, stop, or change direction, along with pace, speed, etc. The sensors gather the metrics, but it is only after the data is put through the company’s complex algorithms (top secret, says Rowe) that the software is able to make sense of the data and present it to you in a meaningful way.

There are a couple of steps you can take to help the sensors out and ensure an accurate distance reading. First, set the devices to reflect the length of the pool in which you’re swimming—25 yards, etc. Secondly, finish laps (no stopping before the wall!) so the devices can register the start/stop motion during a flip turn or touch turn. If you’re wearing the FINIS Swimsense, you should also specify on which wrist you’re wearing the device to improve accuracy.

Going Head-to-Head
When using the FINIS Swimsense, connect the USB dock to your computer and plug in the watch to charge. During this stage, you also register on, check for any software upgrades, and personalize your settings via the free Swimsense Bridge software. Once everything is set up, go for a swim. In theory, the four-button watch is easy to navigate, although it can be a bit confusing until you get used to it. Select “Swim” to begin an interval, press “Pause” during rest, and “Stop” to end your workout. “Reset” stores the workout for later upload.

If you turn on iiM (interval inference mode), you won’t need to manually press the “Pause” button during rest. As long as the Automatic Interval setting is switched on, the sensor will infer and automatically record your rest periods between swim intervals based on non-movement. It’s best to make sure you rest for a good five seconds at the wall (preferably without waving your arms about) to make sure the device registers the rest period. You can distinguish pause mode from swim mode when the screen colors invert, turning the background black and the numbers white.

The Garmin Swim device is ready to go out of the box. It has a replaceable battery (versus a rechargeable one), and there is no need to connect it to a computer prior to your first workout. You will be prompted to set the pool size the first time you enter swim mode. You should also enter your weight if you’re interested in calculating the number of calories you’ve burned.

Garmin Swim has six buttons; icons on the display screen indicate the function of each one. Begin a workout by first pressing the turquoise button to enter swim mode, then pressing the start/stop button. When stopping to rest, press “Pause.” When ready to resume, press the same button.

After a swim, FINIS Swimsense must be plugged back into the USB dock; the solution relies on a physical connection to transfer the data—thus, the device falls a bit short of being truly connected. Garmin Swim, on the other hand, is equipped with ANT+ wireless technology, which can automatically upload data to your Garmin Connect portal when within range of your PC.

To upload data, first go to and follow the onscreen instructions, which include downloading the ANT Agent software, plugging the USB ANT stick (included) into your computer, and selecting “yes” on your Garmin Swim device when it asks if you want to pair it. This only needs to happen once. From then on, when ready to upload, simply place the device within about 16 feet of your computer. Using the ANT transmission protocol, the USB ANT stick will recognize your device and automatically transfer new data.

ANT is a wireless sensor network RF (radio-frequency) protocol suited for ultra-low-power applications like wireless health and fitness devices. It runs using low-cost, low-power microcontrollers and transceivers operating on a 2.4 GHz unlicensed band. ANT+ refers to the added interoperability function on top of the base ANT protocol, which facilitates wireless communication and data transfer among other ANT+-enabled devices in the realms of sport, wellness, and home health. Essentially, ANT+ provides off-the-shelf interoperability. For Garmin Swim owners, ANT+ integration means you get seamless, wireless connectivity, all at a quite affordable pricepoint.

And now, to reveal the winning device. In the size-and-comfort category, the sleek Garmin Swim wins. Battery life is another feather in Garmin’s cap. (Personally, I’d rather replace my battery periodically than worry about constantly charging it.) The FINIS Swimsense’s iiM mode, which enables a hands-off approach to tracking swim/rest intervals, is a big plus for FINIS, as is its status as a pioneer in swim tech. But while I have little to fault FINIS with, in the end, it comes down to connectivity. For that reason, thanks to its ANT+ technology, I’m choosing the Garmin Swim. For busy pseudo-athletes like me, the more connected, the better.