This app was mentioned in 2 comments, with an average of 2.00 upvotes
very cool! looks like it uses the front facing camera to detect a quad over head. Creative programmers never cease to amaze me.
Its not a free app, on android at least: https://play.google.com/store/apps/details?id=com.joshdsommer.WhoopLaps&hl=en
https://play.google.com/store/apps/details?id=com.joshdsommer.WhoopLaps&hl=en android link for the app. Costs $2 it looks like.