I've found a live round in an "unloaded" gun and I've found a hot mag before grabbing a prop! Both are sobering, possibly deadly, experiences and they both happen more than you think.
During shutdown, the procedure drilled into my head when learning to fly was "Mixture, Master, Mags." I can still hear my flight instructor's voice today. And before hooking a tow bar to a plane, I ALWAYS verify "Key out?" NOT "Mags off?" Here's why.
"Mixture, Master, Mags," deplane, grab the tow bar, reach for the prop to turn it so it clears the tow bar. Are the mags off? Are you sure? Of course! You remember turning the key just a second ago. All safe.
Ok, Look at the key. That's not off! That's why the procedure is "Key Out!" and preferably on top of the panel where you can see it.