The instructions warn that you may get more molehills initially as the moles try to escape the noise; you're supposed to move the devices after 3 or 4 days to keep chasing them out of your yard (and into the neighbors', one supposes). Looking at the new mole hills this morning it appears our devices are working well - so well, in fact, that David repositioned them today to keep the moles moving toward the cornfield beyond the tree line that borders our yard. (We're purposely aiming them toward the cornfield rather than our neighbor's yard - although his efforts are probably why WE have so many this year!)
Time will tell whether our new strategy will be successful. We'll keep you posted!