If you hold the phone on your side of the bed, it should theoretically record your sleep pattern, not hers. So it should play the alarm when you’re in light sleep, not her. And since the alarm starts off with low volume, there’s a high chance you will be the first to hear it - she might not even notice it before you’re already up. Unless you’re a heavy sleeper and she isn’t, in which case - yeah, it might not work.