In one aspect of the present invention, a method for managing communications in a sensor network will be described. A coordinator device receives charging interval data from an energy harvesting sensor device. A sleeping interval for the sensor device is determined. A beacon frame is transmitted from the coordinator device to one more sensor devices in a network. The timing of the transmission is based at least in part on the sleeping interval data. The beacon frame may contain requests, commands or other data designated specifically for the sensor device. Various other aspects of the invention relate to the sensor device, the coordinator device and/or their operations.