I have the security pattern enabled on my phone. I was recently on a call and I had an alarm notifying me. I have my alarm option set to persistent. I couldn't dismiss the alarm because it was difficult to get the screen to turn back on, enter the security pattern, and then get into the notification to dismiss it. Maybe we could just make an option to silence alarms (or reduce the volume/turn off vibrate) while on a phone call? You would still get the notification icon.