IPhone – How long does an iPhone alarm last

I have written up a procedure for you to try:

1. Restore your phone.
2. Test - if successful go to last.
3. Take your iPhone to the nearest Apple store and tell them what's happening.
4. Test the issue with the refurbished iPhone they gave you to replace the one that was malfunctioning - if successful go to last.
5. Enjoy your "15 more minutes" feeling.

Failing all of these, your alarm is going off and you're sleeping through it because you stayed up too late playing WoW, drinking, coding, whatever. It eventually stops making noise and leaves the message on the screen. Try placing the phone across the room so you have to get up to turn it off. See if that helps. Either way, now you have a newly refurbished iPhone 4.

Please forgive the snarky nature of this answer. I wrote it after my alarm didn't go off in the morning due to a push notification.

No, unfortunately there is no such setting. Your best bet is probably to use a 3rd party app with alarm clock functionality. That way it will only play the sound through the headphones and not the speakers. The main disadvantage is that you would need to remember to keep the app launched before you go to bed each time.