Switch interfaces typically allow people with physical disabilities access and input into a range of computing devices. They will typically send a keystroke to the device. This can be used to operate the switch control features built into iOS and Android, and software in Microsft Windows based systems. They can form a key part of an Assistive Technology system.
This switch interface based on the Arduino-based Adafruit Feather 32u4 Bluefruit LE development board. These are available from a range of suppliers including Pimoroni.
A work in progress currently using a prototype board!