Wireless sensor networks (WSNs) combine sensing, computation, and communication for automated data collection, processing, and telemetry. WSNs use spatially distributed devices for applications in which scalable connectivity and energy efficiency are increasingly important. Thus, WSNs are a key technology for the Internet of Things (IoT), whether consumer and industrial, connecting billions of devices over the Internet for applications including health care, transportation, process analysis, and environmental assessment, to name a few. However, wireless connectivity comes at the expense of power.