This Japanese iPhone 5S user is using his nipples to lock and unlock the new 5S. It looks like it's not only cat paws that can do the trick. The sensor works on other body parts too!

It's definitely smart, since you can trick thieves into thinking the phone you're holding isn't yours.
According to Japanese site Rocket News, the new iPhones can recognize your nipples.

Check out the video where the iPhone owner registers his nipple and locks the phone with it. A different man tries to unlock the phone with his nipple to no avail. It works!

Let's not stop at nipples. How about toes? No problem too: