If the furnace starts pulling more than 4,000 Watts, I get a telegram message that the auxiliary heat is running instead of the heat pump.
I have a sensor in my kindergartner’s bag that lets me know when he gets to school and when he leaves school, also via telegram message.
If someone loiters around my driveway for more than 30 seconds, I get a telegram message with an image.
I haven’t said it back up since I moved but I used to have one that used a combo sensor my washer and dryer doors. If the sensor moved enough for long enough it set a flag that the unit was running. If it want from running to not running for a long enough period of time, and the contact sensor wasn’t tripped, I would receive alerts every 30 minutes or so that the clothes were done and still in the washer/dryer.
Even something as simple as water sensors under the sink if saved my ass. Cabinetry these days is made out of fiberboard and if it stays wet for more than a couple of hours it does horrible things.