Have bought the Wühlmausschreck to scare a pesky garden dwellers without using chemical additives. The unit of Sonic Repeller makes a good impression. It's now been about 3 weeks in use. Success has not yet occurred. But what stands out: The Wühlmauslöcher have something away from the site where the device is in the ground, but are elsewhere again new surfaced. For advertised range of approximately 500m², this does not exactly .... The Vole gets even a period of 2 weeks. After that, I regret to pick up the vole - She had a fair chance :-)