A popular smartphone app that estimates your blood pressure doesn't provide reliable readings. In fact, more than three-quarters of people with high blood pressure who use the Instant Blood Pressure app will be falsely reassured that their blood pressure is normal, according to a small study that compared the app results to readings taken with a traditional blood pressure cuff.
To use the app, you put the top edge of your phone on the left side of your chest while holding your right index finger over the smartphone's camera. The app—which was among the top 50 best-selling iPhone apps for about five months—is no longer for sale, for unclear reasons. But it's still installed on a vast number of iPhones, and similar apps are still available, according to a research letter published online March 2 by JAMA Internal Medicine. Bottom line: Don't use any app that uses the phone itself to measure your blood pressure.