I need to carry my iPad to classical concerts and other occasions where I can't have it suddenly beeping and alerting. In the settings, there is Notifications On/Off. Probably we can assume that being Off, there will be no beeps whatsoever. Correct? How about if I only put the volume to zero - are any apps capable (including any whacky 3rd party apps) of causing audible alerts if the volume is zero? And finally, if I push the power button for 3 seconds or so and switch off iPad fully, is it capable of alerting me in that state?