On-call?
Don't want the person sharing your bedroom to wake up when you get paged?
If you're a deep sleeper and share a bed with a light-sleeper, this just might be the thing you need to let them keep sleeping after that 1:30am call. Or the thing to let you know you need to check your phone in the middle of a meeting. Either way, sysadmins are a market for this thingy!