One thing that is great about the Galaxy S8 is the fact that it gives you so many options to secure your device. There are all the traditional options such as PIN, Password, or gesture. Samsung also has a few biometric options with the fingerprint scanner and the iris scanner. They have even thrown in face detect for good measure. Each option has its own set of pros and cons. The fingerprint scanner is very accurate and fast. The only issue with it is that it is awkwardly placed right beside the camera. I have been using the phone for a few days now and have missed the fingerprint scanner several times. The face detect option is less secure. You won't be able to secure services like Android Pay because of this. The disclaimer even says your twin could unlock the device, and some people have been able to use a photo to trick it. Face detect also does not work in low light. The best option for me is the iris scanner. Out of the box the iris scanner requires you to swipe up to activate it, but you can actually set it to automatically search for your eyes once the screen turns on without swiping up. If you enable this setting you can just press the always on home button to turn on the screen and activate the iris scanner. This feels very much like using the fingerprint scanner on my older Samsung phones. As far as whether or not it works in low light I have tested it in pitch black darkness and it still works. This happens to be my favorite security setup. What setup are you using for your Galaxy S8?