The paper introduces an extremely simple and ultra low-power time synchronization algorithm mainly tought for Body Area Networks. Time synchronization of different sensor nodes represents an important issue for both real-time and off-line data merging applications. The core of this modular approach is a fractional-timer concept, borrowed from the Phase-Locked Loops theory, and a heuristic routine managing the on/off switching of the radio section of the device. Preliminary results are presented proving the benefits in terms of power consumption and improved precision.