A system of sensor nodes is combined with an RF hub that transmits RF power to the sensors and receives data therefrom. The sensor nodes contain: one or more sensors for measuring indoor conditions, an antenna, an energy storage element, and electronics for powering the system via harvesting RF energy, reading sensor data, and communicating sensor data. The sensors, antenna, and other components on the nodes can be fabricated conventionally, or via printing. They may be fabricated as “flexible hybrid electronics”, in which conventional components are bonded onto flexible substrates. The RF hub consists of one or more antennas capable of transmitting RF power electronics for steering the center of radiation of the RF power in at least one direction or in more than one direction electronics for receiving a demodulating RF data signal. The RF hub may be powered directly from the building.