Alarm goes off indefinitely??

[meikaidi]

Does anyone know if they alarm on the phone with go off indefinitely if its not manually dismissed?? I left my phone at work and am afraid to disturb my coworkers before I return the work in the morning. I am hoping at after 30 minutes it will stop. In the past when I left my phone and couldn't hear an alarm it just kept going off until I hit it off but I don't know if I've let it go past 20 mn. Any help is much appreciated.