I THINK THESE THINGS WORK...
Assembled the units and placed in the yard, all very simple.  I live in an area where moles are very active, especially this time of year.  What seems to be happening is that the critters will still invade and make a mess of my yard, but leave in a day or so.  My conclusion is that they are driven away by the noise of this product.  It doesn't seem to prevent them from digging in, but does seem to drive them out.  So, I have less damage from moles than before but it's not eliminated the problem entirely.
Rating: 4 stars