Twelve subjects with phones in their pockets and in bags they're carrying on both arms were asked to work out using an exercise bike, and then sit, stand and lie down. Unfortunately, the researchers found some inconsistencies when they compared the data gathered by the app to the data from the FDA-approved sensors the subjects were also wearing. The heart rates from the smartphone data were off by more than one beat per minute, while breathing rates were off by a quarter of a breath per minute.

Hernandez admits there's still much to be done before you can toss your fitness trackers -- they still have to figure out how to gather info more accurately, as their experiment proved that the farther the phone is, the less reliable the reading gets. Last year, Hernandez's team worked on a similar study called BioGlass that used the Google Glass' accelerometer, gyroscope and camera to measure heart and breathing rates, as well. Just like that project, one of BioPhone's goals is to be able to detect if you're stressed, so it can suggest some breathing exercises or to call a loved one.

[Image credit: Janitors/Flickr]