Abstract: A behavior modification system includes a network of components that interact to collect various data and provide user feedback. The network may include a personal device, an Internet-enabled storage device and a hub capable of receiving communications from the personal device and communicating to the storage device. The personal device may include bio-impedance measurement circuitry, an accelerometer and a processor for determining energy expenditure based on data from the accelerometer(s). The system may include a smart hub capable of routing communications between various components within the system. The hub may include different transceivers for different communication protocols. The system may incorporate a low-power RF wake-up system. The system may include bio-impedance measurement circuitry that is reconfigurable to function as an alternative type of sensor.