# A Survey on Energy-Aware Security Mechanisms for the Internet of Things
## 1 Introduction
### Importance of Energy Efficiency  
More often than not, IoT devices are deployed remotely or in mobile environments--and the use of batteries to power IoT terminals has become the dominant paradigm today. While the use of batteries to power IoT terminals provides flexibility and independence for the devices, it also presents a number of challenges and drawbacks. First, the battery life limits the long-term operational capability of the device. After all, the battery life is limited, and with the passage of time, the battery capacity will gradually decrease, and providing convenient installation also means that the battery needs to be replaced periodically to ensure the normal operation of the sensor network. Frequently changing batteries increases the difficulty and cost of operation and maintenance. This greatly limits the growth rate of the Internet of Things. Imagine that when billions or even tens of billions of sensors are battery-powered, the labor and material costs of maintenance will become an unpredictable economic burden. According to a prior study [6], the size of IoT nodes will be limited--and hundreds of billions of nodes may not be deployed if batteries have to be regularly replaced. This not only leads to huge maintenance expenses,  
Figure 1: Visualization of the co-citation network of ‘IoT’, ‘energy’, and ‘security’ publications. Reference relationship from 2019–2024. but also has the potential to compromise at least 80% of the value of the IoT. Thus, battery replacement costs pose a significant challenge to the sustainability and economics of a large-scale IoT. Efforts to address this issue have focused on finding more durable and sustainable energy solutions, such as energy-harvesting technologies, long-life battery technologies, and wireless charging technologies, in order to reduce the pressure on battery maintenance costs. Thanks to the advantages of lithium batteries such as a light weight and long life, they have now become the preferred power supply method for IoT sensors. However, with the increasing demand for batteries, the convenience brought by lithium batteries is accompanied by a series of problems. First, there are potentially toxic materials in lithium batteries, posing a serious threat to human health and the natural environment. Second, in order to produce lithium batteries, manufacturers need to mine large quantities of key raw materials such as lithium, cobalt, nickel, manganese, and graphite, a process that consumes large amounts of energy and water resources and often results in chemical pollution and geological damage to the local environment. In addition, batteries can accidentally release cobalt and copper during production and disposal, posing a direct risk to human health [7]. Therefore, despite the significant advantages of lithium batteries in providing energy, the benefits and drawbacks must be carefully weighed in the quest for a more environmentally friendly and sustainable energy sources. In fact, most of the traditional sensors use batteries as the main energy supply method [8], which is obviously a huge consumption of human and material resources. Sensors, as an irreplaceable part of the Internet of Things, have a limited battery life to power them, and in order to guarantee the proper functioning of the sensor network, all batteries need to be replaced periodically to ensure that the sensors continue to operate properly. The battery life depends on factors such as the power consumption of the sensor, its operating frequency, and the parameters it measures. Hence, maintenance personnel need to check the status of the batteries--and periodic replacement prevents sensors from stopping working due to energy depletion. This manual maintenance inevitably involves cost and labor resources, and in some cases may result in temporary sensor failures until the batteries are replaced. In areas that are difficult to reach or require frequent monitoring, such a maintenance becomes more complex and expensive.