A software equivalent could be a GUI program which steers the mouse pointer to the close-button in the window's title bar and synthesizes a click there.

The tricky part seems to be retreating the arm into the box after switching the machine off.

Use a latching relay or something. Not too tricky.

http://en.wikipedia.org/wiki/Relay#Latching_relay

I just love this thing. It's completely perfect and perfectly complete.

Reversing the arrow of time on this kind of thing has provided intellectual entertainment for ages ... Nowadays, the most frequent answer seems to be "In the beginning there was nothing, which exploded" - which may be true but is obviously unsatisfactory to brains addicted to pattern-matching and causality-finding.

Flipping the arrow forwards again, there's the "immanentize the eschaton" angle.

Thanks for the link/article. Shannon is on my "people I admire" list, and I've read some of his papers and looked around in the AT&T site, but this titbit had escaped me before.

Do check the link in the article, http://www.research.att.com/~njas/doc/shannonbio.html (and there's more links in that page): "the man who invented a rocket-powered Frisbee and who juggled while riding a unicycle through the halls of Bell Labs." Ha!