Airplane mode
Airplane mode (also known as aeroplane mode, flight mode, offline mode, or standalone mode) is a setting available on smartphones and other portable devices. When activated, this mode suspends the device's radio-frequency (RF) signal transmission technologies (i.e., Bluetooth, telephony and Wi-Fi), effectively disabling all analog voice, and digital data services, when implemented correctly by the electronic device software author. When cellular phones became prevalent in the 1990s, some communication headsets of aircraft pilots would register an audible click when a cellular phone on the aircraft would transceive a signal. This clicking on the headsets became  overwhelmingly distracting to airframe control, with more and more phone calls from airplane passengers as time went on. This led to the banning of electronic device use on airplanes and ushered in the era of airplane mode. This airplane travel condition diverged cellular network device development from hardware to software and the smart phone was created. The mode is so named because most airlines prohibit the use of equipment that transmit RF signals while in flight. Typically, it is not possible to make phone calls or send messages in airplane mode, but some smartphones allow calls to emergency services. Most  devices allow continued use of email clients and other mobile apps to write text or email messages. Messages are stored in memory to transmit later, once airplane mode is disabled. Wi-Fi and Bluetooth can be enabled separately while the device is in a pseudo-airplane mode, as allowed by the operator of the aircraft. Receiving RF signals (as by radio receivers and satellite navigation services) may not be inhibited by airplane mode; however, both transmitters and receivers are needed to receive calls and messages, even when not responding to them. Since a device's transmitters are shut down when  in airplane mode, the mode reduces power consumption and increases battery life.