A smart device is an electronic device, generally connected to other devices or networks via different wireless protocols (such as Bluetooth, Zigbee, near-field communication, Wi-Fi, LiFi, or 5G) that can operate to some extent interactively and autonomously. Several notable types of smart devices are smartphones, smart speakers, smart cars, smart thermostats, smart doorbells, smart locks, smart refrigerators, phablets and tablets, smartwatches, smart bands, smart keychains, smart glasses, and many others. The term can also refer to a device that exhibits some properties of ubiquitous computing, including—although not necessarily—machine learning. Smart devices can be designed to support a variety of form factors, a range of properties pertaining to ubiquitous computing and to be used in three main system environments: physical world, human-centered environments, and distributed computing environments. Smart homes indicate the presence of sensors and some detection devices, appliances, and a database to control them. In 1991 Mark Weiser proposed three basic forms for ubiquitous system devices: tabs, pads and boards. Tabs: accompanied or wearable centimetre sized devices, e.g., smartphones, smart cards Pads: hand-held decimetre-sized devices, e.g., laptops Boards: meter sized interactive display devices, e.g., horizontal surface computers and vertical SMART boards. These three forms proposed by Weiser are characterized by being macro-sized, having a planar form and by incorporating visual output displays. These were also envisioned more as information appliances. If each of these three characteristics is relaxed, this range can be expanded into a much more diverse and potentially more useful range of ubiquitous computing devices. Smart devices are typically composed of a hardware layer (including a radio that transmits signals), a network layer (through which devices communicate with each other), and an application layer (through which end users deliver commands).