# Efficient Intrusion Detection Algorithms for Smart Cities-Based Wireless Sensing Technologies
## 1 Introduction  
The world is now experiencing a huge change in technology, especially sensing technologies. These emerging technologies lead to new opportunities in industry and economy. At the same time, people are connected through their smartphones, laptops, and tablets. In addition, smart devices, meters, and appliances are used in almost every city. Vehicles and social systems, as well as services, are almost connected, forming an \"internet of things (IoT).\" In addition, researchers and organizations are developing standards and protocols for IoT systems to standardize devices' connections. Consequently, cities are developing their infrastructures, services, control systems, and monitoring systems to accommodate the new changes. Smart transformations, smart traffic, weather, and location services are also connected. Public safety and disaster responders are also integrated. Such connectivity and integrations form a new concept, which is smart cities. However, this uncontrolled growth of the cities brings new situations and issues that need to be taken into consideration by the governments and stockholders. The concept of a smart city depends exclusively on embedded systems, intelligent technology, and sensing technologies. In general, a smart city uses information technology and embedded infrastructure to improve the standard of living. Two of its main issues are security and electronic crime concerns [1, 2]. Three factors affect the smart city securities, which are governess, technological, social factors. The focus of this paper is on the technological factors, which is mainly the sensing technologies. Sensing technologies include different types of sensors and networks where smart sensors are used in many applications. Smart sensors are tiny sensors with limited processing and storage capabilities. They are also equipped with communication and sensing technology, see Figure 1; however, they also remain limited in their sensing and communication ranges because of their extremely limited energy sources. As can be seen in Figure 1, the main components of a sensor node are: (1) the power unit, which is the source of energy, (2) the sensing unit that is used to collect the data from the monitoring environment, (3) the processing unit in which the collected data is processed, (4) the radio unit where the communication takes place, (5) the localization unit that defines the location of the sensor nodes, (6) the mobilize unit is used to help the node move, (7) the actuator unit is used for moving sensors parts, (8) the multimedia unit is used for handling videos and images if needed, and (9) the power generator that is used for energy harvesting, if any. There are many sources of energy that could be used to recharge the sensor nodes, such as WiFi charging units, and mobile vehicle with removable chargers, as well as the advances on solar cells, makes the self-recharging of sensor nodes possible [3; 4]. However, each of those solutions come with a cost in which the size of the node increases as well as its price. Therefore, with the large number of sensor nodes deployed in an application, such as a smart city, sensors budget will not be affordable. One more thing to consider is that wireless sensor networks (WSNs) do not always operate in a safe environment; they might be deployed in a hostile environment that cannot be accessed. Sensors are deployed manually or randomly in the monitored field to monitor the surroundings [5]; they autonomously form a connected network--wireless sensor network (WSN). They usually use self-discovery techniques [6; 7; 8] to discover their neighbors' nodes. Those sensors cooperate to send their sensed information to a powerful node, named sink node. There are various routing and clustering algorithms that are used for such purposes [9; 10]. WSNs are considered as the core network of smart city applications. Once deployed, WSN is supposed to live for a long time without recharging the nodes' batteries.