Despite an explosion of mobile app offerings for management of pain and anxiety, the evidence for effectiveness is scarce . Placebo-controlled trials are the most desirable but designing inactive placebo apps can be challenging . For a prospective randomized clinical trial with 72 patients in a craniofacial pain center, we created an app with self-hypnotic relaxation (SHR) for use with iOS and Android systems . A placebo background audio (BA) app was built with the same look and functionality . Both iOS and Android SHR apps alone and in comparison to the BA group significantly reduced pain and anxiety during the waiting-room time . The Android BA app significantly reduced anxiety but not pain . The iOS BA app affected neither pain nor anxiety, functioning as an ideal placebo . Usage analysis revealed that different default approaches of the iOS and Android devices accounted for the difference in results.