How do I "train" Face Unlock? After updating my UK HTC Sensation to Android 4.0 I was keen to try out Face Unlock.  I'm happy to say that it works reasonably well, however the setup process has led to me having a query.  

When setting up face lock, after your face has been captured for the first time and setting up your backup access, you are given the following prompt:


  You've Finished!
  
  To unlock your phone, just look at it.
  
  Tip: Improve face matching by having your face captured in different conditions


The tip sounds good, however it doesn't actually tell you how to have your face captured in different conditions! After clicking OK to the prompt you are returned to the security menu and any attempt to re-set-up face unlock just seems to over-write your previous settings (or at least I assume it does as it asks you to set up a new backup system).

How can I recapture my face multiple times to improve face recognition?
Go to Settings -&gt; Security -&gt; Lock screen -&gt; Improve face matching.  You will need to confirm your PIN, and then follow the on-screen directions to capture your face again.

After each successful capture you will be placed back to the Lock screen settings menu, so just keep going into the Improve face matching section to repeat the process as many times as you wish.