Google Android allows you to use face recognition to unlock your device. Here is a tip they helpfully provide for using this feature:
TIP: After you set up Face Unlock, look under Settings > Personal > Security for two additional settings: Improve face matching and Liveness check. Use these to make Face Unlock more reliable and secure. [emphasis added]
Such a relief to know that someone can’t use my dead face to unlock my Android device after they kill me.