How can I recover when my iPhone isn't responding to touch when using Guided Access on iOS 6? Is there a recommended solution for when Guided Access fails to respond to triple-click of the home button?  I set this up for a kids app for my son, and despite triple-clicking the home button several times, I am failing to get a response to prompt for my guided access pin number.

I tried holding the power button, and several other options, all to no avail.  Is my only option to let the battery die out?  Will that even fix the issue?
Seems like a solution is to hold home button + volume down + screen lock until device forcibly reboots.  After that, guided access began responding properly again and I was able to exit the app.  

Edit:  Through trial and error, I felt this was home button + volume down + screen lock, but as comments  have noted, volume down is not necessary.