Bio-metric scanners use physiological characteristics to determine who someone is. They can range from fingerprint or vein readers, to iris and retina scanners, facial recognition and even voice. Every person’s physiological makeup is unique to them, whether it be the way their veins are laid out within a hand or whether it be the complex design to their iris. Bio-metric devices are incredibly reliable and very difficult to falsify or trick. As mentioned, due to some of the complexities involved in certain techniques, costs can vary massively depending on what it is you are after.