I've been increasing my lap time by controlling the entry of my hands into the water, less splashy, biggest push at the perpendicular, save your movement to when it moves the most mass.
It's tempting to just go all out and start spraying water like a blender, but that's a waste of energy, ever notice
how little splashing olympic swimmers do?
So that's where this comes in. It's a swim cap with a motion sensor that gives you recording of your head movement so you can chart your progress with a pretty big metric for swimming efficiency which equates to speed.
Easier than balancing a glass of chocolate milk on your head. (link)