An unobtrusive, mobile in-ear pulse oximeter for body sensor network with predictive power-management optimization algorithm is presented. The system can be connected via Bluetooth to a smartphone for online visualization of vital signs, recording or telemonitoring via UMTS (Universal Mobile Telecommunications System). The work focuses on energy saving strategies. Main part of the work is a significant reduction of the PPG-on-time by means of a real-time heart rate estimation routine. The concept is tested on sleep apnea patients with 96.8 % correct estimated heart events at a mean power consumption of 103 mW.