Over recent years, Bluetooth Low Energy (BLE) has found widespread applications in various sectors, including medical devices, smart home technologies, IoT sensors, and wearables. Despite its popularity driven by low power consumption, its security requirements have remained a critical concern. This study conducts a comprehensive examination on BLE security, assessing the effects of different security levels on power efficiency and performance in real-world scenarios. Unlike previous studies which often concentrate on singular aspects of security, power efficiency, or performance, our research adopts a holistic approach by incorporating these factors simultaneously. We bridge this gap by thoroughly exploring the interplay between these critical factors, offering insights into the trade-offs involved and conducting a comprehensive analysis of the cost of security in relation to power efficiency and transmission performance. We evaluate BLE's power consumption under realistic conditions and quantify the cost of security on perspectives of energy and transmission speed. The experimental results indicate that security settings can impact both energy consumption and performance. Moreover, our findings reveal that more performant protocol configurations can paradoxically lead to reduced energy consumption. This highlights the paramount importance of the security-power-performance trade-off in BLE protocol design.