Turning on Android device with motion detector (external device?)
Just to let you know I have some up with a simple solution it combines an app from the app store called Motion Detector by jastrzab: https://play.google.com/store/apps/details?id=org.motion.detector 
Then install a plugin called Turn Screen: https://play.google.com/store/apps/details?id=org.jastrzab.plugin.screen


Install both apps. 
Open the Motion Detector app and turn on "Send" at the bottom of settings. Click on motion detector (at the top) and then scroll down to "camera" and select "front". 
Open the Turn Screen app. click the only button to make it active. 
Open android settings, Turn off the lock screen or select "none".
Change the sleep settings to time out in the desired time. 
Turn off Daydream.
Open the app (or home screen) you want to have displayed on the screen when the tablet wakes, and you're all set! Wait for the screen to go to sleep and walk by or wave at your camera and it will wake it up. 


Works great during the day or with the lights on. I'm currently working on an external PIR motion sensor that will allow the tablet to wake in darkness. Simple design so far just uses a cheap PIR sensor and a small led light mounted below the camera. When I walk by the PIR triggers the LED light allowing the camera to see, which triggers motion. Hoping to figure out how to eliminate the LED and just run the PIR directly into the tablet using the headphone jack or USB on the tablet. Suggestions welcomed.