I have a detached garage, which I have left the doors open on more than once. Got smart and painted the door panels in a checkerboard green/white pattern, so I can easily see if the door is closed when I look out a back window of my house at night.
Worst result of leaving the door open was a very mean stray cat taking up residence for the night, and scaring the crap out of me when I nearly stepped on it the next day while rummaging for some scrap lumber. I had no idea I had so much vertical leaping ability ;-)
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TRAVELLER, SHOULD YOUR ROAD LEAD YOU TO SPARTA, TELL THEM THAT YOU SAW US LYING HERE AS THE LAWS WILLED IT.
-Inscription on a Greek monument to Leonidas and his soldiers