An autonomous battery-free microwave frequency communication device which includes a capacitance, at least one antenna, a microwave energy harvesting system, a microwave frequency transceiver, and a control system. The energy harvesting system is configured to harvest and store microwave energy received via the antenna onto the capacitance. The transceiver is empowered by energy stored on the capacitance, and is configured to autonomously generate a microwave frequency carrier and to autonomously transmit information using the microwave frequency carrier according to a predetermined communications protocol via the antenna. The control system is empowered by energy stored on the capacitance, and is configured to provide information for transmission. Energy may be harvested from various communication forms, such as wireless network protocols or cellular communications. The frequency band from which energy is harvested may differ from the frequency band used for communications. The energy storage enables autonomous communications with external devices according to common or standard wireless communication protocols.