We love this little device. We've been putting the headphones on and hopefully pressing it to my belly since about week 12, and so far we haven't been able to hear anything besides some unpleasant stomach noises.
Two nights ago, that all changed. She was moving around a ton, so I was able to direct Casey to her location, and by a huge stroke of luck, he found her little heartbeat! It was so cool! It's neat to have that one additional sign that she is there and doing well.