Gear change recording Has anyone heard of a device that records gear changes?

Like a cadence sensor or power meter, but specific to recording when you change gear.
With all the data we can currently capture about our cycle training, it would be interesting to see which gears are used and when, mapping this against gradient/speed/cadence/power/... .

While I don't plan on dropping any coin on di2 or etap, is this even something included in them?
No such product exists for mechanical groupsets yet. As for Di2, you just need the little Bluetooth transmitter to communicate with your head unit. This will record the number of shifts, as well as the gear that you're using at any time. 

I've included a screenshot of the Wahoo Elemnt app to show how this data is displayed. To set this up, you need to program your cassette and chainring ratios into the head-unit, because your Di2 isn't able to tell the number of teeth, only which cog it's on.