This is on some android phones, double tapping power will open the camera. I use it all the time to take pictures of information that I don't want to write down, package numbers, measurements, error logs, all just tap tap, point, volume down.
I occasionally use it that way for painted labels on parking-spaces at the airport. (I have yet to need them, but it seems a reasonable precaution given how even a small amount of floor/zone/row forgetfulness could leave me wandering the 10,000-spot complex.)
That said, I also find myself wishing I could mark those photos as "temporary", so that they get auto-deleted within a month or whatever.
