Recent times have witnessed a spate in the use of modern scientific techniques such as the lie detector, brain mapping and narco analysis, for use in criminal investigation. Although the legal and ethical propriety of their use has been in doubt, they may in fact be a solution to many a complicated investigation. This article describes how the techniques may be used against an accused and concludes that although the legal setup in India may limit the evidentiary use of the techniques, their extensive deployment, particularly that of narco analysis, in investigative processes, in itself violates the fundamental rights- against self incrimination, health and privacy of the accused. Courts in India have taken into account an incomplete consideration of the law, which is the reason for their conclusion in favour of the tests. While the tests may be a practical necessity, the sanction of the law for some of them is difficult to find, and extensive safeguards need to be laid out to prevent their abuse. It is now upon the Supreme Court to define the limits of such tests in context of the rights affected, or vice-versa.