In his post on the “great iOS mute switch debate,” Marco Arment mentioned in a footnote that

If only built-in apps were allowed to bypass Mute, we would complain that developers couldn’t make useful alarm apps and Apple was being evil.

Trouble is, it’s only partially true that 3rd party apps can play noises if the mute switch is turned on. Apps that use background notifications for alarms, which is any alarm app worth a damn, can’t play notification noises if the mute switch is on and the app has been exited. However, if the app was the most recently used and you just hit the iPhone’s top “sleep” button, the app can still play noises. That must be what Marco means. I thought this was the case, based on my work on an alarm app that, sadly, changes in iOS 5 made impossible to ship. (Although as I write this I think I’ve thought of a workaround for the app I abandoned).

I also tested it out with Due and Night Stand HD.

The bottom line is that if you want a timer or alarm to go off and ignore the mute switch, no matter what, without worrying about it, you are stuck with the built in iOS Clock app. Which doesn’t suck for the end user, but it does suck for app developers who have ideas for better alarm apps.