Surely we must understand the principle before drawing a hasty judgment: This is not a 120 dB siren will scare pain your visitors. Except perhaps for the birds, but I think that are more sensitive to flash as ultrasound ??? In my case, 2 units of 2 sides of the house. Cats were quickly disrupted and are now distant. The effectiveness is judged in the long term (at least 15 days mini, not six months either!) I served as one of two to also protect a corner of freshly seeded lawn. And here also works. I put in 5, all mode switches successively. Effective for birds, but cats continue to stay away. Drawback of the system, the low-range. For a house of 13m long, it fails to cover the length. However, cats get tired and end up not approach, even outside the area. Battery and solar collector, he rather beautiful home for installation, so here works globally. I still have noticed a "failure" during a rainy day, but the next day refonctionnait clear day ... ??
