Aspects are described for a device comprising a wireless transceiver configured to receive a radio frequency (RF) emission from a source device, an energy-harvesting unit configured to charge the first device wirelessly, using a first part of the RF emission, and a processor communicatively coupled to the transceiver. The processor is configured to modulate the first part of the RF emission based on information detected by the device and determine that an energy level of the device is above a threshold. The processor is further configured to transmit, in response to determining that the energy level is above the threshold, using the wireless transceiver, the modulated first part of the RF emission to the source device. The processor is further configured to transmit, in response to determining that the energy level is above the threshold, using the wireless transceiver, a second part of the RF emission wirelessly to another device to charge the other device.