A sensor apparatus is for a power bus including a plurality of characteristics. The sensor apparatus includes a housing; one or more sensors each adapted to sense a characteristic of the power bus; and a circuit adapted to transmit or receive a wireless signal. A processor includes a low-power mode and a routine adapted to wake up from the low-power mode, to input the sensed characteristic from the one or more sensors, to output a corresponding signal to the circuit to transmit as the wireless signal, and to sleep in the low-power mode. A power supply is adapted to power the sensors, the circuit and the processor from flux arising from current flowing in the power bus. The power supply includes one or more voltages.