So, I like to see a sensor that is just a microphone array that listens for noises.
You could train it to hear anything in your house and it would just sit around and listen for those tones. Then you could buy any old water sensor, doorbell, washer/dryer, fire alarm, CO detector, and get alerts for any of them from one device. Put it in train mode, set off your alarm, record it as what it is.
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