The advancement in medical science and technology has revolutionized human interaction with machines, crafting one of the most promising state-of-the-art technological fields of today's world. This innovation has made doors opened to rehabilitation beyond patient assistance-Brain Computer Interface (BCI) has stepped forward towards life automation (brain controlled daily life actions), and entertainment (hands-free gaming). This paper reviews key techniques and sensors vital to this technological paramount, along with an appraisal to the commercially available sensors. An exclusive appraisal on state of-the-art BCI technologies has also been discussed conferring their application specific importance. The methodical study of these technologies and comparison of corresponding techniques and sensors is potentially useful to demonstrate the significance of brain machine interface.