I think Bembel had some very bright ideas on the German forum.
I'm not writing them here, because I don't want to steal his thunder:)
They played around with the key so that the inserted key in the lock itself reveals wether it's left in the locked position or in the open.
The kwickset looks nice, a pity that it"s kwickset..

Or aren't kwicksets very insecure? I don't know American made locks which are not high security well unfortunately.
Maybe I'd get one if I could change the core in it to abloy or sth.
And I would feel better if the code would supplement the keyed lock but not overwrite it. But I don'T think that's an option. I think it would also be troublesome to install here in Europe.
red and green nail polish
I like that idea! If you want it to make more obvious paint the whole tumbturn half red half green. That's not too aesthetic but is definitely noticable from far away.

a simple circuit with a switch, resistor, and flashing red LED
Squelchtone if you do build it and you deem it DIY-able would you consider sharing it or would you like to sell them or so?