Obstructive Sleep Apnea Syndrome (OSAS) is the most common sleep-disordered breathing disease. Considering its severe effect on human health, long-term monitoring is necessary. However, the current OSAS monitoring systems require patients to stay in the hospital overnight and need considerable amount of wiring around the human body. This paper proposes a smartphone-based, wireless e-health system designed for OSAS, which offers anytime and anywhere monitoring. The study focuses on the energy issues of this battery-driven system, and makes full use of the low-power mode of Bluetooth, which has been proven to be the energy bottleneck, resulting in 50% increase of system lifetime. Compared with current methods for Bluetooth mode switch, this proposal, implemented on smartphone, improves system versatility and expandability, and provides technical support for holistic energy-saving approach based on load balancing among data storage, transmission and computation.