###### Abstract  
Internet of Things (IoT) has been developing to become a free exchange of useful information between multiple real-world devices. Already spread all over the world in the most varied forms and applications, IoT devices need to overcome a series of challenges to respond to the new requirements and demands. The main focus of this manuscript is to establish good practices for the design of IoT devices (i.e., smart devices) with a focus on two main design challenges: power and connectivity. It groups IoT devices in passive, semi-passive, and active, giving details on multiple research topics. Backscatter communication, Wireless Power Transfer (WPT), Energy Harvesting (EH), chipless devices, Simultaneous Wireless Information and Power Transfer (SWIPT), and Wake-Up Radio (WUR) are some examples of the technologies that will be explored in this work. Internet of Things (IoT); Wireless Sensor Networks (WSN); backscatter communications; Wireless Power Transfer (WPT); Energy Harvesting (EH); chipless devices; Simultaneous Wireless Information and Power Transfer (SWIPT); Wake-Up Radio (WUR) +
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0000-0001-5001-50001-5000]R.R. However, to achieve future predictions, several technological challenges need an answer, which may be divided into five significant issues: security and privacy, storage and cloud computing, energy, communication, and compatibility and standardization, illustrated in Figure 1.  
Implementing security processes in IoT devices has a high level of complexity due to the limited capabilities available on the devices, their vulnerabilities are related to transport encryption, inadequate software protection, and insufficient authorization. These risks are threatening data privacy, which is a crucial aspect, especially when considering applications like health equipment and emergency services. The second issue regards storage and cloud computing that relates to the data generated by the increasing number of IoT devices. Currently, the used architectures for data centers are not prepared to deal with the quantity and diversity of data that billions of heterogeneous devices can generate. In addition, there is a need for new intelligent analytics mechanisms; just a small percentage of the data that is nowadays stored suffer a process of scrutinization to obtain valuable information. In the past, these mechanisms were mainly applied in a centralized architecture based on cloud structures; however, nowadays there is a clear tendency to prefer a certain degree of analytics in the edge devices--fog computing. These new decentralized architectures are most important to offload some of the computing and processing tasks occurring in the cloud, allow more efficient use of resources, provide highly responsive services, and enforce privacy policy [3, 4]. Also linked to the number of IoT equipment is the problem regarding energy. Considered by many as one of the leading technological challenges for the next years, the way how energy is harvested, stored, and used will dictate the pace of evolution in the sector. Energy-efficient devices are imperative not only to enable more and more applications but also to make the existent ones greener and more environmentally friendly. Besides challenges associated with energy, it is also essential to consider the way how they communicate, the data rate of IoT terminals could vary from a few kbps to several Mbps, and distances that can vary, from a few centimeters to several kilometers. These specifications need to be taken into account when developing the communication system to achieve efficient use of power and spectrum, minimizing the interferences between communications. Lastly, the compatibility and standardization of IoT systems is a very desirable aspect once it would help all the other challenges already mentioned. Having certain norms would allow all actors to equally access and use, promoting the efficient use of IoT infrastructure and applications [5, 6, 7].