A mobile device (or handheld computer) is a computer small enough to hold and operate in the hand. Typically, any handheld computer device will have an LCD or OLED flatscreen interface, providing a touchscreen interface with digital buttons and keyboard or physical buttons along with a physical keyboard. Many such devices can connect to the Internet and interconnect with other devices such as car entertainment systems or headsets via Wi-Fi, Bluetooth, cellular networks or near field communication (NFC). Integrated cameras, the ability to place and receive voice and video telephone calls, video games, and Global Positioning System (GPS) capabilities are common. Power is typically provided by a lithium battery. Mobile devices may run mobile operating systems that allow third-party Mobile app to be installed and run.
Early were joined in the late 2000s by larger, but otherwise essentially the same, tablet computer. Input and output is now usually via a touch-screen interface. Smartphone/tablet computer and personal digital assistants may provide much of the functionality of a laptop/desktop computer but more conveniently, in addition to exclusive features. Enterprise digital assistants can provide additional business functionality such as integrated data capture via barcode, RFID and smart card readers. By 2010, mobile devices often contained sensors such as , and gyroscopes, allowing detection of orientation and motion. Mobile devices may provide Biometrics user authentication such as face recognition or fingerprint recognition.
Strictly speaking, many so-called mobile devices are not mobile. It is the host that is mobile, i.e., a mobile human host carries a non-mobile smartphone device. An example of a true mobile computing device, where the device itself is mobile, is a robot. Another example is an autonomous vehicle. There are three basic ways mobile devices can be physically bound to mobile hosts: accompanied, surface-mounted or embedded into the fabric of a host, e.g., an embedded controller embedded in a host device. Accompanied refers to an object being loosely bound and accompanying a mobile host, e.g., a smartphone can be carried in a bag or pocket but can easily be misplaced. Hence, mobile hosts with embedded devices such as an autonomous vehicle can appear larger than pocket-sized.
As stated earlier, the most common size of mobile computing device is pocket-sized that can be hand-held, but other sizes for mobile devices exist, too. Mark Weiser, known as the father of ubiquitous computing, computing everywhere, referred to device sizes that are tab-sized, pad and board sized, where tabs are defined as accompanied or wearable centimetre-sized devices, e.g. smartphones, and pads are defined as hand-held decimetre-sized devices, e.g., . If one changes the form of the mobile devices in terms of being non-planar, one can also have skin devices and tiny dust-sized devices. Dust refers to miniaturised devices without direct HCI interfaces, e.g., micro electro-mechanical systems (MEMS), ranging from nanometres through micrometers to millimetres. See also Smart dust. Skin: fabrics based upon light emitting and conductive polymers and organic computer devices. These can be formed into more flexible non-planar display surfaces and products such as clothes and curtains, see OLED display. Also see smart device.
Although mobility is often regarded as synonymous with having wireless connectivity, these terms are different. Not all network access by mobile users, applications and devices need be via wireless networks and vice versa. Wireless access devices can be static and mobile users can move in between wired and wireless hotspots such as in Internet cafés. Some mobile devices can be used as mobile Internet devices to access the Internet while moving but they do not need to do this and many phone functions or applications are still operational even while disconnected to the Internet. What makes the mobile device unique compared to other technologies is the inherent flexibility in the hardware and also the software. Flexible applications include video chat, Web browsing, payment systems, NFC, audio recording etc. As mobile devices become ubiquitous there, will be a proliferation of services which include the use of the Cloud computing. Although a common form of mobile device, a smartphone, has a display, another perhaps even more common form of smart computing device, the smart card, e.g., used as a bank card or travel card, does not have a display. This mobile device often has a CPU and memory but needs to connect, or be inserted into a reader in order to display its internal data or state.