Handy Gallery Attendant tip: Hold keys to avoid falling asleep fully.

See, this is why you hold a bunch of keys loosely in your hands. 

Then when you drop off too much, you drop the keys and wake yourself back up.

Handy Gallery Attendant tip #65

(I never did this, I spent dull time copying artwork and sketching visitors, but one gent on our staff had perfected the art of not quite being fully asleep with the key trick. We sometimes wanted to cordon him off and label him as an exhibit.)

Image from here