Thought and thought, about why are there flys in the house.? Seems the buggers were just circling round under the front porch, and when you open the door, they come in. Why do supermarkets seem to be fly-free? Answer is they use this device. So, bought it, mounted it, plugged it in and voila, 99.9% fly-free, no strips, sprays, swatters, no mosquitos either. Satisfied. Wife agrees. Happy wife, happy life. Worth it.