Maybe some sort of generic bluetooth sticker with some integrated sensors for temperature, sound level, motion, orientation, pressure. Slap that bad boy on the side of your washer, and register it on your phone. Adjust its parameters to alert when conditions are met. Noise and vibration means its going. Use this data to build a fuzzy profile of what a wash cycle looks like in duration, volume, shakiness etc. Alert phone when we think cycle is done.

Smack another sticker inside your fridge. Alert if temperature exceeds x degrees for n minutes.

Boop another onto your stove. Temps above x when youre not cooking mean someone left it on.

Yeet a few more outside. Periodic increases in volume mean the dog is barking when you arent home.