title: Sl4a recognize speech in background
body: <p>I am started programming sl4a (in QPython) and it is really great. Now I tried to use the droid.recognizeSpeech function. This one works fine too, but I like to get it in the background listening for a keyword, like Google's 'OK Google'.
  So I looked around, but cannot find anything. I don't know how I can implement it.
  So I ask you, can someone tell me, if it is possible, how to make recognize speech always listening in the background waiting for a keyword?</p>