So I'm on my laptop playing League with headphones on while I'm on iFunny in the comment section when the [fire] alarm-like sound started to sound. I looked down at my phone thinking it was a video, but I realized I was in the comment section so the sound couldn't have been coming from my phone. So I turned my phone off. I then look around in an attempt to find the source of the sound. I looked at the fire alarm in my room, but the alarm wasn't there (we needed to get new batteries). Then I looked at my DS and it wasn't coming from there or my laptop. So I grabbed my phone and put it to my ear. The sound was coming from it. I was afraid because my phone was off and it wasn't a notification sound. In fear that it might explode, I put it at a distance from me.
My best explanation for the sound was a fire alarm sound that kept repeating. (No it was not an amber alert noise either).
Why was my phone making that noise? Should I be worried?
Extra Info: I have an iPhone 6 and it was not charging when I was using it.