Just a couple years ago, fitness trackers were basically glorified step counters worn on your wrist. Now, they’re doing everything from measuring your heart rate on a run to notice you to get out of the sun. And they’re the world over. Every company from Fit bit to Jawbone and Microsoft makes a beautiful advanced piece of wrist-worn technology now — all with the guarantee of better health.

But what’s in these things, anyway?

Even though fitness bands are rather simple compared to advanced smart watches, a growing number of sensors packed full inside has turned them into multipart labs on your wrist. For example, Microsoft’s Band advertises 10 dissimilar sensors in the little package. With potential higher than ever, bands are getting extremely technical and complicated to compete.

These are the sensors inside, making it happen:


The most familiar and basic tracker included is the accelerometer. It can be used for multiple things, but is naturally put to work counting steps. By measuring direction and acceleration force, they can find out whether the device is horizontal or vertical and whether it’s moving or not. Not all accelerometers are created equivalent. You’ll find both digital and analog ones, different sensitivities, and unlike numbers of axis. The very basic ones will only have two axis, while three-axis sensors can calculate their position in three dimensions. At this point, most fitness trackers use quite advanced accelerometers for increased fitness tracker accuracy.


GPS is decades-old technology, but its look in fitness bands is comparatively new because the chips are becoming more efficient — nobody wants an enormous band on their wrist to accommodate a massive battery. GPS is still fairly power hungry compared to supplementary sensors. The worldwide positioning system comprises a network of 29 total satellites orbiting the globe — at any place, a person should be in range of four satellites needed to pinpoint an accurate place.

The GPS recipient receives a high-frequency, low-power radio indication from the satellites. The time it takes for a signal to accomplish your wrist can be translated interested in your distance from the satellite, which can be translated into precise coordinates with data from adequate satellites. GPS chips continue to get better at handling battery usage, but GPS is still quite power hungry compared to other sensors. Unlike simple footstep counting, GPS allows runners, walkers and cyclists to simply map their exercise and evaluate the terrain where they were excising.

Optical heart-rate monitors

Unlike the EKG a doctor might use to measure your heart rate, an optical heart-rate monitor calculate your heart rate using light. An LED shines through the skin, and an optical sensor examines the light that bounces reverse. Since blood absorbs more light, fluctuations in light level can be translated into heart rate – a process called photo plethys mography.

Galvanic skin response sensor

Galvanic skin retort sensors measure electrical connectivity of the skin. When internal or external forces cause stimulation — of any kind — the skin becomes a better performer of electrical energy. Fundamentally, when you start to sweat, either from exercise or something else, the band will be capable to monitor that. An LED shines through the skin, and an optical sensor examines the light that bounces reverse.

Detecting when someone is sweating gives the software more information about what a client is doing, which allows for better health tracking. Being able to associate the level of activity with a different source than just gravity from the accelerometer, allows these programs to get on a more trainer-like role — recommending specific exercises and levels of physical exertion.


Even a basic thermometer can supply valuable information by way of your skin temperature. Rising skin temperature can point out to a fitness band that you’re exerting yourself, or if your heart rate isn’t growing accordingly, that you might be getting sick.

Ambient light sensors

Ambient light sensors are all around us. For instance, one tells your phone to mute its screen at night and brightens it in the sun. A fitness tracker uses it for the same function, and for detecting the time of day.

UV sensors

Instead of telling your fitness band how light it is around you, UV sensors tell it when you may be engrossing harmful UV radiation – usually from the sun. Software compares this data to the values familiar by scientists to be harmful, and warms you to get out of the sun if you’re likely to burn.

Bioimpedance sensors

Jawbone’s new UP3 wrist band uses a single bioimpedence sensor to cover up three bases: respiration rate, heart rate and galvanic skin response. According to the company’s own blog post explaining the technology, “The sensor measures very tiny impedance changes inside your body. For heart rate, we are measuring the impedance changes formed by the volume of blood that is flowing in the Ulnas and Radial arteries. The same sensor, worn around the wrist, will also be competent to tell respiration and hydration by looking at metrics like oxygen in the blood. It does this by using four electrodes that drive a tiny bit of electrical energy to each other, and then measuring the results.


These sensors may supply a fitness band with reams of data about your heart-rate, body temperature and even altitude, but it’s not value much without software to translate it into useful advice. From anticipating illness to spurring you on to more implement tomorrow, it’s all of these sensors working jointly that truly provide a clear picture of your health today, and what you can do to develop it tomorrow.