Is it possible to increase the strength of the alarm vibration?
apparently not,
under android.os.Vibrator, you can set the pattern as well as the duration
vibrate(long[] pattern, int repeat)
vibrate(long milliseconds)
my guess is that different patterns can be used to "simulate" a stronger vibrate. (on,off,on,off) rather than (on, off, off, off, on).
also a disharmonious pattern may be more effective than a pattern with a fixed rhythm.