Owing to the advancement of vibration energy harvesting technology, many motion-powered battery-free Internet of things (IoT) applications have been reported in recent years. Since the ambient energy is usually weak, these IoT devices (a) mostly operate in intermittent or burst mode. The operation of these devices heavily depends on the level of stored energy. Conventional energy-aware solutions are carried out based on discrete general-purpose comparators or analog-to-digital converters (ADC) inside the system on chip (SoC) to monitor the storage level. Their power consumption is considerable in a low-power system. This paper presents a new energy-aware circuit, which can wake up or turn off the IoT devices according to the stored energy. Its standby quiescent current is at the sub-$\mu$A level. The proposed circuit also provides a regulated output voltage for IoT applications. This design is built with discrete analog components. It is low cost and has high feasibility. It is compatible with different kinds of micro-power generators.@en