Volume button != power button. Nobody ever hammers on the power button repeatedly.
I've done this lots of times. On my phone, volume up and power are on opposite sides. I've often tried to turn the volume up without looking and wondered why nothing happened.
You haven't seen some tech illiterate people try to work a phone have you?
That's something my mom would do. She once asked me how you can tell if the phone was on or off... no joke.
Tech illiterate people probably aren't the ones to install a panic button application for use by demonstrators.