I’m seeing this problem:
Siri works fine the first time I try it after a restart, but on the second and subsequent tries, when I press and hold the home button, the screen turns gray and the microphone icon is displayed, but there's no sound and no wavy line indicating that input is occurring. The discussion is detailed here. Some claim that Siri will only work via bluetooth. This appears to be happening on iPhone 5/5S hardware
Is there a workaround?