Ivan StepaniukAfter a quick recording with my phone, the Audacity frequency plot reveals that my dishwasher end-of-cycle tones are at 3.969 kHz.
At first I thought that it was probably 4 kHz and my measurement had some error, but no, it's exactly 3.969 kHz. Probably, the MCU inside the dishwasher is using an imprecise RC clock generator, or perhaps this tone was easier to obtain by dividing the MCU clock. In any case, it's different enough from 4 kHz to take it into account when detecting the tones. Nobody wants the dishwasher opening when the microwave beeps!
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