Smartwatches and other wearable devices can almost feel magical. Tied to a Fitbit, Apple Watch, or Samsung Gear, suddenly a stream of data generated by your body appears: step count, heart rate, blood oxygen levels, calories burned, and more.

Wearable devices provide tools that help people monitor and understand their bodies, thus promising to improve their lives. Apple CEO Tim Cook even said that technology companies are eager to save your life.

As a professor of research technology, I have been researching smartwatches and other wearable devices over the past decade. My new book, “Bringing orders: Wearable Technology and Manufacturing in Everyday Life,” considers the gap between these product commitments and what they actually do.

Wearable devices rely on sophisticated sensors and computer systems to create data for each user. As these devices become more common and more complex – I’m worried that people might think less about how they work. As a result, they may accept data of face value without considering the way it is generated, whether it is accurate or not, and can even put them at risk.

So, in order to get the maximum from wearable technology, it is worth reflecting on the difference between what these devices seem to do and what actually happens behind the screen. These are a few key points to remember.

1. Steps are not real steps

The wearable fitness tracker gained popularity in the early 2010s for its ability to calculate steps and measure distance, calories burning and stair flights, among other measures. While it is easy to think of the so-called step count reflects the number of times the wearer's foot completes the action taken by the step, this is not the case.

In fact, a combination of sensors and algorithms together generates a data point called a "step." In most cases, the so-called accelerometer measures changes in wearable speed. This is checked against an algorithm that provides an automatic evaluation of whether sufficient speed has been reached to treat it as a step. These components measure the degree of movement of wearable, not the movement of a person. Shaking your wrist quickly sometimes produces a "step" and walking in place may not be able to calculate the steps.

2. Some skin tones don't work like other shades

Blood oxygen sensors have become many smartwatches. They use a process called Photographysmmography, which uses tiny green LED lights at the bottom of a smartwatch to track how blood flows through your wrist.

In 2022, Apple's lawsuit is allegedly continuing racial bias because its blood oxygen sensors don't work well on darker skin. The case was dismissed in part because researchers and doctors have known about these limitations of blood oxygen sensors over the years. In other words, people think that certain functions don't work for some people.

3. Your location may not be a secret

The entire industry is made up of people called data brokers who buy large data sets from technology companies and sell them to advertisers, market analysts, or other groups that may be interested in getting them.

While some companies have taken more steps to reduce or eliminate data sharing with third parties, and government agencies provide users with strategies to limit location sharing, others may still share data between branches and service providers.

It is important to check all settings to reduce or eliminate data sharing options. Otherwise, your private information may not remain private for a long time. For example, in 2018, practice app Strava released a “heat map” showing running and cycling routes through which all users gathered—and unexpectedly disclosed the locations of multiple secret military bases around the world.

4. Consumers' wearables are not medical grade

With wearables, just like other technologies, be sure to review the terms of use carefully.

Most devices contain boilerplate language about how to use the data they provide in entertainment, and cannot replace the doctor's formal diagnosis. Even if Apple has already obtained FDA licenses for some health testing features and they can be very useful for surveillance purposes, it is important to consult a doctor if you rely on data for health purposes.

5. Wearable devices cannot predict the future

OK, maybe this should be obvious. But that's not.

The pioneering measurements of the OURA ring, such as "recovery" attempt to measure your sleep, have recently added a "symptom radar" to try to detect when you get sick.

These techniques use sensors, such as heart rate monitors and thermometers, to detect changes in the wearer’s baseline. While predictions of these diseases may be helpful, they are like the body’s weather reports, using available sensors and algorithms to detect changes in the atmosphere inside the human body. Any claim to predict the future is based on finding patterns in past information.

While wearable technology can provide powerful insights, understanding how devices work is critical to understanding the data it produces. A little skepticism goes a long way: it can challenge exaggerated commitments and protect users. Finally, it is best to understand wearables as fun but imperfect tools – not magic wands.