Actigraphy for Better Sleep?

I previously questioned the efficacy of the Zeo "Personal Sleep Coach" and concluded that this device would be unlikely to provide their claimed sleep improvements.

Another method for monitoring sleep patterns is with the use of Actigraphy*. I seriously doubt that these movement-based devices can do any better:

• Wrist-worn accelerometer: WakeMate (HT MedGadget) and Axbo.
• iPhone under your pillow: Sleep Cycle alarm clock (see Sleep Cycle iPhone App VS WakeMate Bracelet))

At least the Zeo device uses an EEG-based sleep histogram for determining sleep state. How can the acitigraph tell the difference between someone just laying awake quietly versus deep sleep?

*This Wikipedia entry reads like an advertisement for one these devices!