Active implantable medical devices (AIMD) play an important role in monitoring, diagnosing and treating patients. In-body medical device development has been facing an increasingly stronger demand with increases at a pace of 6% yearly. The current technical challenge in this field is creating smart, small and long-term use implants that improve the patients’ health and life quality. In this context, while implanted power sources have been almost exclusively based on traditional batteries, mechanical energy-harvesting devices exhibit clear advantages and could be used in many AIMD in the near future. Using the example of the pacemaker, this talk presents technologies and strategies to efficiently convert mechanical energy into electricity, highlighting the main challenges that need to be addressed in the particular context of the human body (low vibration frequency, extreme miniaturization, high reliability) as well as the technological and methodological evolutions required to move towards industrialization of implanted biomechanical energy harvesters.