I have started with Speech recognition using android, sl4a and python and so far, it works fine. My user is just supposed to input numbers between 0 and 9 with his voice. Is there a way to tell android to only search in those number and therefore reduce the time of recognition (and probably errors) ?
No. You cannot change what google returns. You can only process the results.
Fortunately, you can process the results to increase the chance of a match.
For example, you could use a phonetic matching algorithm like Soundex
Using Soundex or something similar, if the recognizer hears something like "true" your code could still recognize it as the number 2.
来源：https://stackoverflow.com/questions/8778409/speech-recognition-reduce-possible-search-results