I downloaded and installed facelock.apk on my Motorola Android tablet (running 4.0.3) but it fails with "Face unlock couldn't start.".
What's the reason? What can I do to get it working?
See Goo.im. They have a collection of Google Apps as installable .zip files.
There is an explanation for which packages belongs to what Android version on top.
However there's currently only one separate package for Facelock.
The Facelock.apk may not be compatible or rather, clearly, missing some dependency with the Motorola's version of the framework.
It could well be modified to exclude the facelock application as well. To each and their own, each manufacturer are free to modify, add, subtract from the Google Android source to suit themselves.
It might help to obtain the