An increasing number of persuasive technology systems consist of multiple devices that enable efficient just-in-time interaction with the user. Developing multi-device systems to support a human activity bring about new challenges for interaction and user experience design. The main challenge identified in this paper is the successful designing of coherent user experience, which may improve user acceptance and have a positive effect on the overall persuasiveness of the system. This paper analyses a multi-device heart-rate monitoring environment to illustrate the target of our research. We propose the notion of distributed user experience as a key concept for studying the design of efficient persuasive technology systems consisting of multiple devices.