If you think you are going to be arrested, turn your phone off. Then back on. It requires your passcode before the sensor will work again. . . or don't have it on your person, leave it in your car. They have to get a search warrant for your car and by the time they get that it will have cycled and then also require a passcode. In addition, they have to get another search warrant to have you apply your finger to any such devices not found on your person.