I use a suunto ambit 2s to check my jump height, aldo this sport watch have accelerometers, I only could program an APP in this watch which manages GPS data with some others defined variables. The basics of this App is measuring the mean tide level (by retrieving the last 15 seconds of the lowest gps height) and then calculates the difference between the jump height and the mean sea level.
I think this is not very accurate but at least you can have a reference when jumping and for progressing... This is a video I made about this...