A Brain-Computer Interface, or BCI, describes a system of interaction between a machine and an organic neurological system. The aim of a BCI varies by application. Currently, Brain-Computer Interfaces are used to augment or repair cognitive or motor functions in humans that have lost the ability to control parts of their bodies. In these cases, BCIs act as restorative technologies. As BCIs become more afforadble, more accurate and easier to use outside of medical facilities, their use will increase. Outside of the medal realm, BCIs may be used for entertainment in the form of video games, for communication in the form of conferencing and social networking, and for remote control and sensing of networked objects.
Steve Fairclough considers BCIs as "brilliant candidates for assistive technology and effective usage of a BCI device feels slightly magical – because it is the ultimate in remote control". However, he adds, "like muscle interfaces, all we have done is create an alternative route for human-computer input. The exciting subtext to BCI use is how the user learns to self-regulate brain activity in order to successfully operate this category of technology. The volitional control of brain activity seems like an extension of the human nervous system in my view (or to be more specific, an extension of how we control the human nervous system), albeit one that occurs as a side effect or consequence of technology use".
Non-invasive BCIs allow one to interface with technology without surgery.
Two of the most interesting types of non-invasive BCIs are subvocal recognition, or SVR, and electroencephalograms, or EEG. An EEG device is a non-invasive BCI that works by detecting neuro-electrical transmission in the brain. This neuro-electric brain activity can be converted into various outputs such as the movement of virtual objects, data entry, and the use of a computer without the use of a cursor or keyboard.
Another method of non-invasive BCI is subvocal recognition. Subvocal recognition is a method that allows one to communicate without speaking. In 2008 the Ambient Corporation demoed a device that attached to one's neck and detected subvocal signals, turning them into sound. 
Invasive integrate directly with the nervous system through a mechanical installation and require a surgical procedure in order to be installed. Invasive BCIs are almost exclusively used in medicine as restorative healthcare. They are unstable and too expensive to be used in normal everyday life as commercial products. In order to become stable, everyday products they will have to go through safety testing, become small and cheap enough to be mass-produced, and run software that helps to solve everyday human problems.
- Fairclough, Steve. The Extended Nervous System. Physiological Computing: where brain and body drive technology. Published 6th January 2010. Accessed Oct 2011. http://www.physiologicalcomputing.net/?p=291
- On February 26, 2008 the Ambient Corporation demonstrated what it called the world's first voiceless phone call. Press Release: Ambient Corporation. Accessed Oct 2011. http://www.theaudeo.com/.