With recent advances in AI, many technology firms and developers are exploring whether Generative AI (GenAI) tools can help improve productivity, code quality and the overall developer experience. Current evaluations primarily depend on subjective questionnaire data or code quality metrics. A supplemental objective, continuous, real-time developer-centered measure is missing. Wearables with body sensors that measure the physiological activity of a person have the aforementioned benefits. With their help, impeding factors from GenAI tools on a developer’s well-being and cognitive load may be detected. Implications for productivity may be deduced from these cognitive load measures. This research aims to use body sensor data to (1) assess the ability of wearables to measure developers’ cognitive load in their everyday working context to then (2) evaluate developer experience, productivity and GenAI interactions in real-life work environments. A holistic mixed-method approach by combining subjective and objective measures in a developer-centered manner is taken.