The Internet of Things technology revolves around the core concept of integrating sensors into everyday objects and using connectivity to facilitate the exchange of information that is used in a variety of applications [1]. There are more everyday objects available than people, so the amount of connectivity that IoT devices hold is enormous [2]. In order to better understand the future of IoT technology, it is important to understand the unique circumstances that brought IoT to this point. A key distinction to make between the internet and the IoT is that the internet is a mesh of networks, whereas the IoT network is an interconnected network of devices ^[3][4][3,4]. An early example of the first IoT device was John Romkey’s creation, which enabled a toaster to be turned on or off over the internet in 1990 [5]. It is clear that Internet of Things devices have come a long way from their humble beginnings, and there are many factors that influenced this rise. These devices play an important role in people’s daily lives and involve the handling of massive amounts of data [6]. IoT devices can be seen as a network of interconnected devices that involves sending and actuating devices that provide the ability to share information across different platforms ^{[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]}[7,8,9,10,11,12,13,14,15,16,17,18,19,20,21].

2. Healthcare Applications

The Internet of Medical Things (IoTM) is an emerging subfield that is changing the way healthcare is being delivered through the use of IoT technology (Joyia). The use of IoT technology in healthcare has come a long way and continues to be a promising area for growth. Essential innovations, such as the AliveCor heart monitor, which relies on IoT sensors, show how useful technology can be when applied to healthcare in efforts to save lives ^[22][84]. Advances in technology have consistently played a major role in the healthcare industry, and IoT devices have found numerous applications in healthcare settings. One way that IoT devices are useful in healthcare is through the use of remote health monitoring in order to monitor patients at home rather than in hospitals ^[23][85]. The information that is collected from IoT devices is helpful in medical settings because it can be analyzed and used in ways such as early disease prediction ^[24][86]. IoT sensors even played a critical role during the COVID-19 pandemic in helping healthcare workers better monitor critical parameters that could save lives if changes were detected right away ^[25][87]. By examining these different IoT device applications in the healthcare industry, researchers can find additional ways to advance this field of research. The use of sensors is critical in the delivery of healthcare services ^[26][88]. Sensors in medical devices act as a bridge between the physical and information worlds by collecting a variety of data. Sensors are crucial in helping healthcare professionals monitor different vitals that are important to measure in order to understand a person’s health situation and act accordingly. Medical sensors can be used in a variety of ways in order to measure crucial information. Medical sensors are connected to IoT, and measure things such as temperature, respiration, heart rate, weight, skin conductance, galvanic response, blood flow/SpO2, glucose testing, muscle contraction, and motion analysis ^[27][89]. The medical sensors are connected to wireless sensor networks, which relay useful information to different stakeholders involved in healthcare, such as patients, medical staff, insurers, and more ^[28][90]. The use of medical sensors is vast and can be used in crucial medical equipment, such as ECG monitors, glucose level sensing, and oxygen monitoring ^[29][91]. The goal of using any technology involved in healthcare is to promote better health outcomes, and IoT devices play a critical role in promoting this. Recent advances in IoT-related technology will continue to play a large role in creating stronger healthcare systems, and the future of healthcare will become increasingly reliant on technology ^[30][92]. Medical sensors are important in collecting useful information about a patient’s health; however, this information is often very sensitive in nature, and this makes privacy a major concern moving forward. Security has always played a vital role in IoT technology; however, it matters even more in a situation such as healthcare, where IoT devices will be collecting sensitive information about patients that is private in nature ^[31][93]. If a patient’s medical information was compromised, this could lead to consequences for hospital organizations that did not employ the proper security measures to prevent it. The privacy and confidentiality of a patient’s medical information are core concerns when addressing the security vulnerabilities of healthcare IoT devices ^[32][94]. There are many issues that present challenges to the successful use of IoT devices in healthcare and it is important to address these issues thoroughly when handling mission-critical operations, such as that of healthcare. Some important limitations that influence the use of IoT technology in medical devices include the need for high power consumption, the availability of limited resources, and handling security issues from the large number of devices being used ^[33][95]. The use of IoT technology in healthcare is promising and exciting. There are many useful applications where IoT devices can be used as sensors, and this helps healthcare providers in a variety of ways. Moving forward, IoT technology will continue to expand, and this will ultimately benefit healthcare organizations.

3. Agriculture Applications

As the population of the world grows at an exponential rate, the need for efficient food delivery systems is becoming a core issue that is a driver behind the advancements in smart agriculture ^[34][96]. In addition to the growing demand, factors such as climate change and water scarcity have also played roles in the increasing demand for more efficient agriculture systems ^[35][97]. Much of the technology around IoT implementation aims to reduce agricultural resource waste ^[36][98] as shown on Figure 1. The use of IoT technology in agricultural settings is critical to maintaining efficient operations and represents another common use case of IoT technology. Food supply chains that deliver quality and quantity are important to feed the world, and having efficient systems built around these supply chains will benefit people all over the world ^[37][99]. The need for more efficient food-delivery systems has helped to promote IoT use in agriculture because stakeholders saw the benefits that technology could provide ^[38][100]. One way that IoT technology can be used in agriculture is automation. Automation involves having devices/objects respond automatically to different conditions without the need for human interaction. Wireless sensor networks are key proponents in helping IoT devices achieve their automation goals ^[39][101]. This can be useful in massive operations, such as agriculture, because of its sheer scale and need for efficient processes to maximize crop yields. For example, many sensors can be used in the soil of farmland in order to measure soil moisture content, in order to build systems that make better use of water for irrigation purposes ^[40][102]. These IoT devices can be used to measure soil conditions, such as water content, give appropriate signals when it is low, and turn on sprinkler systems automatically. Real-time monitoring and responses are very common and useful when understanding how IoT devices contribute to agriculture ^[41][103]. Data analytics is another area where IoT plays an important role in agriculture. Collecting and analyzing data are very useful because they can give important insight into how effective or ineffective an operation is. These data can be used to provide stakeholders with important insight that will ultimately impact their decision-making ^[42][104]. IoT devices collect massive amounts of data, and these data are useful when analyzed over time to help aid in decisions about estimation and forecasting ^[43][105]. The gathered data can be analyzed using machine learning methods that impact prediction, storage management, decision-making, farm management, and precision farming ^[34][96]. These data can become useful when attempting to implement more sustainable farming methods through the use of data-driven decision-making ^[42][104]. Although there is a large demand for efficient agriculture, there are other factors in play that have affected the proliferation of IoT devices in this sector. One key component that affects how widespread IoT devices are in agricultural applications is how costly it is to implement them in farming operations around the world ^[44][106]. Massive farming operations would require a large number of wireless sensors to collect data about a farming operation, and this can drastically increase the costs associated with implementing IoT in agriculture ^[45][107]. There are also many technical challenges that exist with implementing IoT technology in farms. Farms are often in large areas that are isolated and usually have poorer signals that impact their networking capabilities ^[46][108]. In addition to this, many farmers in rural parts of the world have limited knowledge of how to use IoT devices ^[47][109].

4. Smart Home Applications

Smart home applications represent promising use cases in which people benefit from IoT technology and there are numerous advantages/disadvantages to consider. Smart home devices date back to the 1970s when the X10 protocol was first conceived; this technology allowed for smart home devices to communicate properly ^[48][110]. IoT devices in smart homes can be used in a variety of ways, such as measuring home conditions, managing home appliances, and controlling home access ^[49][111]. Home automation remains a core feature around which IoT technology is applied ^[50][112]. For example, there are numerous home appliances that can be turned on and equipped with IoT technology in order to become more efficient and convenient ^[51][113]. There are many benefits that extend beyond convenience. The use of IoT sensors in smart homes can be used to assist the elderly in turning hard-to-reach devices on/off and even detect falls through the use of floor or camera sensors ^[52][114]. The market is being driven by the rising popularity of smart devices, such as speakers offered by Amazon and Google. According to a recently released report by Strategy Analytics, the global smart home market has had a positive outcome in recent years ^[53][115]. The report further estimates a compound annual growth rate (CAGR) of 10% from 2018 to 2023, leading to a market value of USD 155 billion, as shown in Figure 2. There are many techniques utilized in order to bring smart home technology to life. One important method relies on radio frequency identification (RFID) systems in order to act as enabler technologies for IoT ^[54][116]. RFID is an important technology that helps in identifying objects, recording data, and even controlling individual targets through the use of radio waves ^[55][117]. RFID devices can be used in a variety of ways. For example, higher education institutions can utilize RFID technology in student identification cards ^[56][118]. RFID technology is also used to detect the indoor roaming activity of elderly individuals and the data collected are used to provide more insight into the health of elderly individuals who live alone ^[57][119]. In an ideal future, IoT devices would be able to seamlessly communicate together [7]. There are many challenges that exist in the use of smart home IoT technology. Interoperability is one issue because the cost of using smart home technology is important to consider, and the integration of devices is a concern moving forward ^[58][120]. Different technologies utilized by IoT devices in order to create this connectivity include Wi-Fi, ZigBee, Z-Wave, Bluetooth LE, and Thread ^[59][121]. Security and privacy are also important to consider because smart grid technology can be a target for cyber attacks ^[58][120]. There are so many IoT objects that can be used in homes, and the dynamic and heterogeneous nature of smart home environments presents a challenge when it comes to addressing authentication and privacy issues ^[60][52]. Cyber attackers could target items such as smart home routers, gateways, or any other IoT-enabled devices to access data ^[61][122]. Many strategies are currently being analyzed in order to address smart home security needs. Blockchain is becoming increasingly utilized because of its benefits of having a decentralized database based on cryptographic techniques ^[62][55]). Although blockchain approaches have benefited from decentralized security/privacy, there are drawbacks when it comes to the energy and computational overhead that make it not ideal for IoT devices that are resource-constrained ^[63][123].

5. Smart Cities

Internet of Things devices have many useful applications when it comes to smart cities. A smart city can be understood as a city that is equipped with technology, such as wireless sensor networks and actuators that collect data; it is used to make important decisions in city operations ^[64][124]. These systems are inherently complex due to the large number of devices, link layer technologies, and the different services involved in the operation of smart city technology ^[65][125]. The smart city concept consists of sensing networks, heterogeneous infrastructure, and information processing systems working together in order to improve a variety of areas within cities ^[66][126]. The use of IoT technology to enable smart cities is useful due to the quality of life it provides for the citizens within those cities ^[67][127]. The goal of smart cities is to use all of the information that is collected from IoT devices in order to improve the performances of urban services to citizens and also consider resource consumption at the same time ^[68][128]. Traffic monitoring is a very important application within the realm of smart cities. It is very common for metropolitan areas to be highly populated, and this causes congestion problems within these cities. Smart cities make use of information communication technologies in order to use the information to make decisions on how to dynamically handle traffic flow ^[69][129]. A smart traffic system (STS) involves real-time data collection and requires IoT devices to quickly obtain real-time public traffic data and have it processed ^[70][130]. The sensors used in smart traffic management systems can be embedded into roads in order to detect vehicles every 500 or 1000 meters ^[71][131]. Cameras are able to apply digital image processing techniques and, consequently, apply algorithms to aid in the prediction of traffic density; this information is then used accordingly ^[72][132]. Aside from helping traffic flow, smart traffic management systems also help with improving air quality and providing safety for the elderly ^[73][133]. Research indicates that the amount of solid waste will reach around 3.4 billion tons by the year 2050, and that will put a tremendous strain on municipal waste management systems ^[74][134]. Smart waste management is another growing application of IoT technology in smart cities. Nowadays, waste management systems are overtaxed and burdened due to the large demands of highly-populated urban areas ^[75][135]. The goal of smart waste management is to use IoT devices in order to optimize waste collection and reduce the negative impact on the environment ^[76][136]. Major factors driving the need for smart waste management include the demand for energy-efficient processes and the goal of creating healthier environments within cities ^[77][137]. A number of different objects can be repurposed into IoT devices, such as trash and recycling containers ^[78][138], and different technologies can be used to indicate when it is time to service a full container. In addition to detecting when waste bins are full, some sensors are capable of detecting unpleasant smells using gas sensors ^[79][139]. These smart containers essentially work by having sensors in the containers that read, collect, and communicate information about the amount of trash/recycle volume within them in order to better understand when it is time to empty the container ^[80][140]. In environmental sector applications, IoT technology has emerged as a valuable tool in enhancing air quality prediction through edge-based computation. Leveraging edge-based computation, IoT devices equipped with sensors collect real-time air quality data at the source, enabling precise prediction models tailored to specific locations. This empowers environmental monitoring systems to deliver accurate and timely information for effective decision-making and pollution control measures. In the realm of anomaly detection and classification, IoT devices continuously monitor and analyze data from diverse sources, swiftly identify deviations from normal patterns, and recognize potential threats or irregularities. Through advanced machine learning algorithms and localized data processing, IoT systems can rapidly detect anomalies, ensuring the robust security and integrity of IoT networks and the data they generate. Moreover, multisensory data fusion in multi-application wireless sensor data streams enables the integration of information from various sensors and applications, enabling a comprehensive understanding of intricate IoT environments. By combining data from disparate sources, such as temperature, humidity, and air quality sensors, IoT systems acquire a holistic view of the surroundings, generating valuable insights into informed decision-making across a wide range of applications, spanning from smart cities to industrial automation.