From Marcin Wichary's Unsung:

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Old-school computing has the term "molly guard": it's the little plastic safety cover you have to move out of the way before you press some button of significance.

Anecdotally, this was named after Molly, an engineer's daughter who was invited to a datacenter and promptly pressed a big red button, as one would.

Then she did it again later the same day.

You might recognize molly guards from any aerial combat movie you ever watched:

And some vestigial forms of molly guards exist everywhere in civilian hardware, too: from recessed buttons, through plastic ridges around keys, 

to something like a SIM card ejection hole:

Of course, molly guards happen in software, too: from the cheapest "are you sure?" dialogs through extra modifier keys (in Ctrl+Alt+Del, the Ctrl and Alt keys are the guards).

But it's also worth thinking of reverse molly guards: buttons that will press themselves if you don't do anything after a while.

I see them sometimes, and always consider them very thoughtful. This is the first example that comes to my mind:

There is no worse feeling for a programmer than waking up, walking up to the machine that was supposed to work through the night, and seeing it did absolutely nothing, stupidly waiting for hours for a response to a question that didn't even matter.