I've been a bit frustrated by the inconsistent activation of the display on my Watch. This may play a role in the inconsistent performance of Siri responding to voice commands. Here's something I've come to realize. When you raise your wrist to activate the Watch display, not only do you need to raise and turn it toward your face but the bottom edge must be near level to activate and stay on. If the lower edge is past 45 degrees, it turns off prematurely. Level your Watch and it will stay on for the preset duration. Not ideal in all situations and it makes it much more obvious that you're checking something. In these cases, a finger touch is more appropriate and the display will activate regardless of your wrist position AND stay on for the preset time.