[We haven't had any new "Random _____ of the Day" threads in a while, so I figured I'd give it a shot]
One of my latest toys is the JR East smartphone app (JR東日本アプリ). It gives you all kinds of information about JR train status. Sadly, in Japanese only.
But what I really like is the "TrainNet" feature. There are speakers above the door in many JR trains now (all Yamanote line trains seem to have it), and these speakers constantly transmit a high frequency audio signal that humans can't hear. But your smartphone microphone can pick it up, and the app receives data from the train this way. Here are a few screenshots I took:
I especially like the 2nd one. The outside temp is 29 degrees. I'm in car 9 where it's 25 degrees and not as crowded as car 5 and 6. Car 4 has decreased air conditioning and is to be avoided by sweaty gaijin like me at all costs. Car 11 is wheelchair-friendly. The other screenshot shows my current location, has travel times to other stations, and you can click through to get station details like location of coin lockers, lists of facilities available, etc.
Recommended for people who are picky about their commuting conditions.