The Internet of Things (IoT) is considered the enabler of the fourth industrial revolution as miniaturised self-powered wireless sensors underpin: e-health, wearables, smart agriculture, food safety/security, advanced manufacturing, resource-efficient and safe transport, and in general the well-being of people in urban and rural areas. If energy management in these 'miraculous' ICT devices can be resolved, large energy savings (and reduced CO2 emissions) can be delivered by using ICT for resource efficiency and optimisation. To achieve long lifetime and small form factors as required in applications, emerging autonomous sensors need to maintain ultra-low power duty cycles and incorporate an energy harvesting source, an energy storage device and electronic circuits for power management, sensing and communication into sub-cm scale systems. A continuous challenge for every implementation and deployment is the gap between energy requirements for operation and energy supply from harvesting sources and storage to enable truly autonomous wireless devices. To bridge this gap, apart from lower energy switching technologies step changes are also needed to advance energy harvesting, storage and micropower management solutions for the integrated design and deployment of miniaturised autonomous sensors.