I saw this post on reddit.com/r/htcone
If you have an alarm set and your phone is powered down, the phone will boot up into Airplane Mode and set off the alarm. I'm running Android 4.3 with Sense 5.5 on my HTC One. This is such a useful feature. Just wanted to share it with the community. I'm thinking it's a Sense feature because I can't get it to work on an HTC One with Cyanogen. This feature should be built into all custom roms if possible!
If you have an alarm set and your phone is powered down, the phone will boot up into Airplane Mode and set off the alarm. I'm running Android 4.3 with Sense 5.5 on my HTC One. This is such a useful feature. Just wanted to share it with the community. I'm thinking it's a Sense feature because I can't get it to work on an HTC One with Cyanogen. This feature should be built into all custom roms if possible!