Something that has some merit.
You know you've taken a big step in your relationship once your SO knows your phone's password. And although you trust them entirely, that doesn't mean you won't look through their phone once in a while when they're taking a dump or passed out asleep.
But then the pesky fingerprint scanner changed all of that. Unless you are a reverse sleight-of-hander who's able to get people to touch things unknowingly (like their hearts), you're not getting into their phone.
Well, that is, unless you've got some Play-Doh lying around. Then you can totally do it.
http://distractify.com/geek/2016/02/26/mustafa-iphone-play-doh