Wearables have the potential to transform healthcare. They can help to inform timely, data-driven interventions. But validating each new digital measure is time-consuming, intensive, and complex. Using open-source algorithms can dramatically streamline this process. Geoffrey Gill at OWEAR describes examples of how wearables can improve healthcare; the challenge of adopting wearables in medical applications; and the benefits of and barriers to using open-source algorithms in wearables.