Iris vs Face

Today, I tried to change the Samsung S8 unlock from face to iris. There were a few things about face unlock that were frustrating:

• It often failed to detect a face
• Even retrying didn’t work
• It would unlock while entering the passcode

With iris scan, there were a few things that were a bit more appealing:

• There’s an indicator light showing you its working
• When it doesn’t work, it’ll give instructions on what to do to improve performance
• It’s fast
• It shows you what it sees so you can adjust the position

More testing needs to be down to see how it functions over time but one question: why can’t face and iris be used in conjunction for either a fall back or for more security?