In this paper, we present a novel Digital Medicines program used for reviewing medication adherence. The program is comprised of an ingestible sensor embedded inside medication and a wearable sensor or patch worn on the skin of the patient. The ingestible sensor activates upon contact with gastric fluids and communicates information about the ingested drug to the patch. Adherence patterns and other physiological markers measured by the system are made available to patients, physicians, and caregivers via mobile and web interfaces. The paper focuses on the wearable sensor hardware and measurement features used to provide a more comprehensive view of the patient's health centered around and contextualized by adherence patterns. This is achieved using efficient, high-performance signal processing algorithms implemented on a low-power platform. Results from bench and clinical testing are presented to demonstrate the performance of adherence, heart rate, step counts, and body angle measurements.