Abstract: Described are apparatus, systems, and methods that are operable to conserve battery power of a wearable device by monitoring a state of the user wearing the wearable device and adjusting power state of one or more components of the device based on the determined user state and/or altering a wireless transmission of sensor data collected by the wearable device from the wearable device to a portable device associated with the user. For example, if it is determined that the user is in a sleep state, the wireless connection between the wearable device and the portable device may be terminated, the wireless transmitter and the processor transitioned to a low power state, and sensor data stored in a buffer memory of the wearable device until a defined period of time before the user exits the sleep state and/or upon satisfaction of a buffer usage threshold.