Early detection of infection symptoms and contact tracing are playing a vital role in containing COVID-19 spread. Multi-sensor and connected wearable devices might enable symptom detection and help tracing contacts. This paper presents the design and implementation of a fully open wearable platform called H-Watch. It has been designed to include several sensors for COVID-19 early detection, multi-radio for wireless transmission and tracking, a microcontroller for processing data on board, and finally, an energy harvester to extend the battery lifetime. Experimental results demonstrated only 5.9~mW of average power consumption, leading to a lifetime of 9 days on small watch batteries.