How about we just crowdsource a DIY WakeMate? The hardware part is just a microcontroller, bluetooth transceiver, and 3-axis accelerometer powered by a watch battery. Sure, the package will be kinda huge when you build it yourself unless you're adventurous enough to etch a PCB and wavesolder it. The firmware just needs to periodically dump buffered samples over bluetooth and let an external app do the heavy lifting.

I should make clear that I'm not knocking on the WakeMate guys at all. Making a production-quality product at scale is a lot harder than hacking something together in your basement.