 Fingerprint sensors have become the new normal, no need for keys or even all fingers. It works by shooting a light at your finger and capturing the light reflected off of it. Then using that image, it can plot a bunch of dots along the finger ridges. And using those dots, you can create patterns that are specific to a single finger. So every time you scan your finger, it will compare it to the saved patterns from before. And if they match, you can lock or unlock anything.