Wireless body-area networks (WBANs) have revolutionized the way mobile and wearable computers communicate with their users and I/O devices. We investigate an energy-efficient wireless device driver for low-duty peripherals, sensors and other I/O devices employed in a WBAN to communicate with a more powerful central device. We present an extensive comparative study of two popular WBAN technologies, 802.15.1 (Bluetooth) and 802.15.4 (ZigBee), in terms of design cost, performance, and energy efficiency. We discuss the impact of tunable parameters of the wireless device driver on connection latency and energy consumption for both Bluetooth and ZigBee. We address dynamic resource management in higher-level protocols by investigating the trade-off between connection latency and energy consumption. We propose an energy-efficient power-down policy that utilizes the interval between consecutive connection requests for energy reduction; we study an adaptive connection latency management technique that adjusts various tunable parameters dynamically to achieve minimum connection latency without changing the energy consumption level. Our measurements and experimental results show that these techniques are very effective in reducing energy consumption while meeting connection latency requirements.