I can't hear
- my doorbell when I'm in my shop
- the dryer's mechanical chime when I'm upstairs
- the oven's little buzzer when I'm out of the kitchen
- which smoke alarm is going off (hearing aids don't have much sense of direction.)
How can an RPi Zero listen for a certain sound or frequency, and then trigger some remote notification? By WiFi? SMS? Other RPis with flashing lights and text displays?
I want to put one near every audio alarm in the house, to act as a relay.