Steampunk GPS
Christopher Fahey on the watchclock, a device built to keep track of the movements of night watchmen.
The mechanism itself has barely changed for a century: although some more recent models incorporate GPS and other technologies, the mechanical key-based watchclock system is still in wide usage, with many buildings still employing the same keys and the same clockwork devices they've used since the 1940s. It's a genuine example of an "if it aint broke, don't fix it" kind of technology.
(via df)