When I first got this app, I couldn't understand why it wasn't showing up on my dock. Stupidly, I kept trying to open it, and even downloaded it again. After giving up, I just looked up at my menu bar to fix some wifi stuff and saw 4 new icons exactly the same, and guess what they were.. iAlertU.
Anyways, long story short, I just set it to password activation in the preferences, so all you do is click the icon in the menu bar, click Arm, and type in the password. And to simply turn the alarm off, just type the password in again.
Enjoy!