I had bought years ago 2 of these devices in Conrad and am convinced that they act. With approximately 2,500 square meters of land, the two were sufficient. I have only my habit to hit the holes for the vibrators with a stake in the ground, because then the earth is compacted and the vibrations are transmitted better. But be careful, do not hit the vibrators into the ground !!! The material is very high quality (aluminum / plastic) and the motors also operate properly after years!