Try an accelerometer with a resolution of 3660µg and a measurement range of ±5g (49 m/s2). I am working on these babies: lucidcode - Halographs.

The software is available as freeware - let me know if you need help writing a plugin for Lucid Scribe for the hardware you end up with.

And if you are just looking for something that blinks or plays recordings throughout the night you can try Liquid Dream.