A new algorithm can help physical activity tracking apps on smartphones provide accurate data no matter where the phones are carried, U.S. researchers say. The apps, which can be a tool for doctors who want to collect data and create treatment or intervention plans, are generally carried in a pocket, on a belt or in a purse or bag throughout the day by patients who are not aware that where they carry their phone can impact how well the tracker works, they said. Now a new algorithm developed at Northwestern University -- designed with fashion and comfort in mind -- can be used with a physical activity app to predict the location of a phone throughout the day with near perfect accuracy, a university release reported. "While it remains true that smartphone activity trackers are the most accurate when the phone is placed in the pocket or on a belt, with this algorithm we can provide an estimate of error associated with other locations where the phone is carried," lead study investigator Konrad Kording said. It is unrealistic to expect all patients with activity tracker apps to always carry their phone in their pocket or on a belt, the researchers said; in everyday life people carry their phones in different ways. "Most women carry their phones in a purse," Stephen Antos, first author of the study, said. "Some people carry theirs on their belt or in their hand. We may change where we carry our phone throughout the day as well. We wanted to solve this problem and find a way to make these trackers as accurate as possible no matter where you carry your phone." The researchers developed a computer algorithm to predict where a phone is being carried and to detect second-by-second activity such as sitting, standing and walking. "I believe we will have apps running on smartphones that will know exactly what we're doing activity-wise and will warn us of diseases before we even know that we have those diseases," Kording said. "In the future, phones will have a major role in motivating people towards behavior that is good for their health."