Policeman at the elbow

The policeman at the elbow test, also known as the irresistible impulse test, is a test used by some courts to determine whether the defendant was insane when he committed a crime. It is a variant of the M'Naghten Rules that addresses the situation in which the defendant knew that what he was going to do was wrong, but had no ability to restrain himself from doing it. The test asks whether he would have done what he did even if a policeman was standing at his elbow, hence its name.