While tracking apps may monitor a person's steps, researchers warn users of heart rate app that results are not what they appear. A study, published in the European Journal of Preventive Cardiology, analyzed popular heart rate tracking apps on performance and accuracy.

The study included 108 patients who measured heart rates by ECG and pulse oximetry. These results were then compared to measurements taken with an app using contact with the user's fingerprint and a non-contact app using the phone’s camera.

"Heart rate apps come installed on many smartphones and once people see them it is human nature to use them and compare their results with others," said last author Christophe Wyss, a cardiologist at Heart Clinic Zurich in Switzerland. "The problem is that there is no law requiring validation of these apps and therefore no way for consumers to know if the results are accurate."

Results found significant variations in the accuracy of the apps, showing differences more than 20 bears per minutes when compared to ECG in 20 percent of all measurements. The non-contact apps where less accurate than contact apps and often overestimated heart rates, especially in patients with high heart rates and low temperatures

"While it's easy to use the non-contact apps—you just look at your smartphone camera and it gives your heart rate—the number it gives is not as accurate as when you have contact with your smartphone by putting your fingertip on the camera,” said Wyss. "Consumers and interpreting physicians need to be aware that the differences between apps are huge and there are no criteria to assess them. We also don't know what happens to the heart rate data and whether it is stored somewhere, which could be an issue for data protection."