An MIT tech company, Cardiio has developed an app designed to spot a. fib. The app uses smartphone’s camera to measure hear rate by noticing slight changes in skin tone. The app is not yet available to the public. The app will be called Cardiio Rhythm. It will be able to look at either one’s face from a distance or at the finger’s skin when it placed right over the camera. It is also designed to estimate the amount of blood pumped by every heartbeat from very slight differences in skin tone and to pick variations in the amount of blood pumped. Two studies have tested the accuracy of the app. One study had shown that the app results were 95% consistent with EKG results. A larger study produced the same results. This article does not cite the two studies that tested the app. My worry is that along with the correctly identified a. fib there will also be a high rate of false positives. This will cause unnecessary emergency department visits. My other concern is that if people depend on this app and something goes wrong with the phone this can have deadly consequences. Mobile devices can be such a great asset to our patients, but we must be careful in knowing their limitations.