How to tell what's restarting my phone?
Found this info from other forums, hope it helps.  Possibly a bad app design, water damage or a bad battery.  

"Restarts are kernel panics. It happens regularly and at random in Android 2.x but is hardly seen in versions 4.x and is caused by many things. One is a full dalvik cache and other times 3G can cause it via a corrupted PRL list update that crashes the modem and takes the kernel with it. (Turning off 3g or if running a custom ROM like CyanogenMod turning force 2G networks on and see if this cures it). I haven't had random restarts on 4.x but deal with them at least twice a week in Gingerbread. I always blamed it on Gingerbread having poor task management built in while 4.x patched it. On one device the 3G auto-PRL GSM mode caused it, while using EDGE and no auto-PRL fixed it but at the expense of speed."
  From: http://www.helpbuildweb.com/post-2072506-My-Android-phone-get-automaticaly-restart..-whats-the-problem-and-how-to-fix-it

Also this seem to be good http://vinner.hubpages.com/hub/Android-phone-is-restarting-How-to-solve