Not one of these firms succeeded in copying our product. These appliances have almost disappeared from the market. This is the way an 'old hat' is sold to the unsuspected end user as a high-tech product. As the mathematical formula for air movement is uncertain, there is no analysis which can differenciate between a break-in and strong wind gusts. When a window is opened 100 times one gets 100 undefined single impulses which differs in shape and size.
Tilted windows are prone false alarms.
Every building has its own room resonance frequency. This tone swings with the resonance frequency of the air volume determined by the volume of the flute. These are mathematically defined sinus-like oscillations. The more holes that are opened the deeper the tone is. Whilst with musical instruments the resonance frequencies lie within the audiable range, room resonance frequencies in buildings are below the hearing range in the so-called infrasound range.