How Does a Biometric Fingerprint Scanner Work?

There are three main sensor types. Optical scanners shine light on the finger and capture a high-resolution image of the ridges using a camera sensor. Capacitive scanners (used in most smartphones) have an array of tiny capacitor cells; ridges touching the surface create different capacitance readings than valleys, mapping the pattern electrically. Ultrasonic scanners (like Qualcomm's 3D Sonic Sensor) emit ultrasonic pulses and measure the reflected signal, creating a 3D map that can read through water and contaminants. The captured image is converted into a mathematical template — a set of minutiae points (ridge endings, bifurcations) — and compared against stored templates. No two people share the same fingerprint pattern, and even identical twins have different prints.