Electronic monitoring devices are increasingly used in healthcare to monitor health behaviors on a day-to-day basis. As a prerequisite to their application in clinical studies or daily practice, the performance of those electronic monitoring devices should be tested. Such testing includes a demonstration of technically correct function and of correspondence between the recorded data and the actual patient behavior, that is, objective testing of reliability and validity. Furthermore, from the patient's perspective, the operation of these devices should be easy to learn and to perform, and their use should be acceptable. These aspects of usability need to be tested from a user's subjective point of view. We propose a conceptual framework that builds on existing literature, for example, the framework on "obtrusiveness" of Hensel et al [J Am Med Inform Assoc. 2006;13(4):428-431], the assumptions regarding valid electronic monitoring of Denhaerynck et al [BMC Med Res Methodol. 2008;8:5], and empirical evidence. The framework integrates an objective and a subjective dimension. The objective dimension encompasses both reliability (accuracy and precision) and internal and external validity. The subjective dimension describes the user's perspective on usability along subdimensions of user performance, satisfaction, and acceptability. This framework can be used as a road map to test existing and future electronic monitoring devices before their widespread application in clinical studies or daily practice.