Power management of sensor nodes is essential to maximize the lifetime of wireless sensor networks, Energy consumption of individual sensor node differs greatly depending on its type. Existing operating systems for sensor networks typically leave the power management of sensors to applications. Unless specific features of the sensors and batteries are considered in the application design, energy consumption may increase or the application may malfunction. In this paper, we define factors to be considered for sensor-specific power management, and then propose an automated sensor-specific power management system. The system is implemented on the multi-threaded RETOS operating system for sensor networks. The experiment results with various applications show that the proposed system reduced the energy consumption by up to 29% without modification of the application code.