How GPS Watches Function

Imagine having a tool that can track exactly how much effort you invest in your workouts. What if you knew every step you took, every stroke of a kayak paddle, or each turn of a bicycle pedal was optimized to help you achieve your fitness goals? How much time could you save? And wouldn't it be more enjoyable to glance at your wrist for precise navigation and weather information?

Unless you've been living completely off the grid for over a decade, you're aware that this isn't a sci-fi concept: global positioning system (GPS) technology has completely transformed how we navigate the globe. At the heart of this system are 24 satellites orbiting the Earth in carefully calibrated orbits. They transmit synchronized signals simultaneously, which devices like airplanes, cars, and even smartphones use to pinpoint their location relative to the satellites. If your GPS device picks up signals from at least three satellites (four is better), it can determine your latitude, longitude, speed, and altitude with remarkable precision, down to a few feet or meters.

A wide range of manufacturers are now applying this previously classified military technology for various purposes, including creating increasingly precise navigation tools and utilizing mobile phone GPS tracking to tailor advertising campaigns for users in specific locations. Sporting goods brands have eagerly embraced this trend, developing a growing collection of GPS watches aimed at athletes and outdoor enthusiasts.

These wristwatch-sized devices are often loaded with a wealth of position-related data; you can now buy a GPS watch that will pinpoint your location anywhere on Earth just minutes after unboxing. But GPS watches aren't just about 'look where I am' features. With a bit of understanding of how they work, you can train more effectively and perform at your best during competition. There's no need to wait for the future of sports and fitness -- it's already here, and it's on your wrist.

The History of GPS Technology

GPS traces its roots back to the dawn of space exploration. The principles that led to its creation emerged when American scientists raced to track Sputnik, the satellite launched by the Soviet Union in October 1957. Drs. William Guier and George Weiffenbach from Johns Hopkins University's Applied Physics Laboratory found that they could monitor the positions of early satellites by studying the Doppler Effect: Signals from a moving satellite would distort as it moved toward or away from the receiving station. By analyzing the extent of the distortion, they could calculate the satellite's orbit.

APL researcher Frank McClure proposed that the tracking system could also function in reverse: By monitoring a satellite with a well-known orbit and analyzing the resulting Doppler shifts in its signal, someone on the ground could pinpoint their own location wherever the signal could be received. The U.S. Navy expanded this concept into the Navy Navigation Satellite System, which began actively guiding ships by 1964. (For more on GPS history, see our article on How GPS Receivers Work.)

Research sponsored by the military continued through the 1970s and '80s, with scientists focused on improving the signal's accuracy, reliability, and speed. The method shifted from Doppler shift tracking to triangulation and signal timing: The longer it took for a signal to reach the receiver, the farther the satellite was at that moment. By the 1980s, GPS was an essential tool for all branches of the U.S. military and its allies, and the U.S. government started allowing civilian access to the technology [source: Parkinson].

Initial civilian GPS devices were bulky and heavy, limiting their practicality for mobile users. However, they faced an even bigger issue: They were not very accurate. To prevent adversaries from using the navigation signals, the U.S. military employed dithering: deliberate interference with the satellites' timing signals to prevent unauthorized decoding. This caused civilian GPS accuracy to be limited to about 300 feet (100 meters). It wasn’t until 2000 that the U.S. government lifted the dithering, allowing for precise civilian navigation. From then on, GPS became an invaluable tool for anyone needing to determine their location, speed, or directions [sources: Parkinson; Navigon].

That solved the accuracy problem, but how did manufacturers manage to make GPS devices small enough to be portable?

The Incredible Shrinking GPS Unit

The advent of dither-free GPS coincided with a revolution in electronics miniaturization—just think about how much lighter a modern laptop computer is compared to one from 1996. GPS engineers seized upon innovations like surface mount technology (SMT), which involves directly soldering tiny components to a circuit board (instead of using wire leads), and robotic assembly, which helped reduce the size of timing and signal processing chips at the core of GPS receivers to nearly invisible dimensions. Today, they're almost too small to see without magnification [source: Poole].

Researchers also applied fractal geometry—which uses self-repeating, scalable patterns—to further shrink GPS units. This allowed for the creation of powerful receiver antennas that could fold into incredibly tiny spaces. This crucial (once bulky) component of the GPS receiver now fits into the sleek casing of a smartphone—or even inside the body of a watch [source: Rusu and Baican; Mikkola].

The first GPS watches were essentially miniature versions of handheld GPS units, measuring about 2 to 3 inches (50 to 75 millimeters) long and about 1 inch (25 millimeters) wide, complete with wrist straps. While they were smaller and lighter than many GPS units of the early 21st century, they were still bulky enough to make running long distances with one—let alone popping over to the coffee shop after a workout with one strapped to your wrist—more of a hassle than it was worth for many athletes [source: Wollman].

Sports that rely on knowing one’s position relative to a target, like golf, quickly adopted GPS during this period of miniaturization. For instance, renowned golfer and course designer Greg Norman became an adviser for GPS product company Inforetech in 2002 [source: GPS Industries]. But it took two major technological developments before GPS watches gained widespread consumer adoption.

Making GPS Watches Practical

To become genuinely functional (and marketable), GPS watches had to evolve to resemble traditional watches. This milestone was reached around 2010, and by 2012, GPS watches had adopted the size, shape, and style of any typical fashion watch on the market. Some models, like a 13-millimeter (0.51-inch) thick prototype released by Epson in February 2012, were even more compact than several non-GPS sports watches [source: Tucker].

However, smaller size didn’t mean fewer features, and this is where GPS watches truly became invaluable training aids. Knowing your exact location is useful, but unless you’re lost in the wilderness or trying to pick the right club on an unfamiliar golf course, the utility is limited. Manufacturers recognized this and enhanced their products by incorporating features from other sports devices, including bike computers, pedometers, and heart rate monitors.

Many GPS watches can wirelessly sync with other devices through signals like ANT+, a small, power-efficient system. These additional devices often track biometrics, such as heart rate, helping athletes assess the intensity of their workouts. Other sensors integrated into GPS watches include shoe-mounted cadence monitors that measure a runner's stride rate and bike-mounted sensors that detect wheel speed and pedal force. The software accompanying these watches allows users to download a wide range of workout data, either wirelessly or through a USB port. By inputting basic details like height, weight, and age, the tech-savvy athlete can have a precise, sport-specific tool—a modern version of the athlete’s training log.

The real value of a GPS watch comes from the combination of location data and biometric information. However, with the multitude of options available, it’s easy to feel overwhelmed. GPS watches come at a variety of price points, with some models ranging from $100 to upwards of $400 as of early 2012. While not inexpensive, how do you decide which GPS watch best suits your needs?

Choosing the Right GPS Tool

Much like you wouldn’t buy a sailboat to navigate rapids, choosing the right GPS watch depends on your intended use. Do you need one for a specific sport, or would you prefer a multi-functional device? Is your priority tracking and analyzing data over time, or having real-time access to information in the field? Do you venture into areas where getting lost could be dangerous, or are you mostly sticking to well-marked paths? Answering these questions will help narrow down your options.

For example, if you're an enthusiastic hiker or cross-country skier who enjoys exploring remote areas, a GPS watch with a moving-map display would be extremely beneficial. This feature shows your position relative to other waypoints, though it comes with a trade-off: the larger screen required to display maps might make the watch too bulky for those seeking a sleek, lightweight option for marathon training [source: Geek.com]. Similarly, athletes who participate in rugged sports like skiing or mountain biking may want to avoid watches with touchscreens, as these could get accidentally recalibrated by a tree branch or other unexpected impact. A runner, however, might find that a touchscreen is ideal for quickly checking their data.

GPS watch manufacturers typically list their features on their websites, making it easy to compare prices and specifications across the market. However, to get a better sense of what might work best for you, it’s a great idea to get hands-on advice. Visit your local bike shop, running store, or outdoor outfitter, and don't hesitate to ask friends for their insights. The firsthand tips and real-world experiences you gather will give you the confidence to select the right GPS watch for your activities.

Making the Most of Your GPS Watch

For those who enjoy outdoor activities like backcountry hiking, sea kayaking, or hunting, the benefits of GPS are clear. These compact devices are specifically designed to help adventurers navigate the wilderness with a reduced risk of getting lost. However, it's always wise to carry a map and compass as backups — countless stories in adventure lore recount incidents where GPS devices failed when most needed, often due to battery issues.

Fitness enthusiasts and athletes can also take advantage of GPS watches to explore new running routes or track their progress while traveling. This is just the tip of the iceberg in terms of how these high-tech gadgets can enhance training routines.

A GPS watch offers a level of performance measurement that was once reserved for researchers and elite athletes. While it's useful to know how long it took to complete a half marathon, a GPS watch can pinpoint exactly where you were the fastest — and where you slowed down. With the data download feature that's standard on most models, you can track trends over time, such as noticing that you lose speed after Mile 10 or struggle with hills compared to last year’s runs on the same course.

Once you identify weak points in your performance, a GPS watch can provide real-time feedback to help make your training more targeted and effective. Take cyclists, for example, who typically focus on building cardiovascular strength during the preseason with longer, steady rides. This establishes a solid base for more intense sprint and hill workouts later on. Relying on a "moderate pace" based on how you feel can be inconsistent. But with a GPS watch that integrates data from heart rate monitors, cadence sensors, and wheel speed sensors, you can fine-tune each segment of your ride, ensuring that you stay within your desired range of speed, heart rate, and time.

The benefits of this kind of focused training can be significant. If you're pressed for time, you can maximize the effectiveness of every minute spent working out, reducing the need to worry about balancing sports, family, and work commitments. When competition day comes, you'll know exactly how much you can push yourself, whether you're on a race course, trail, or track. This technology helps you train smarter, not just harder.