Hot water temperature
I would love to be able to see the temperature of water in my hot water tank. Having a connected water tank thermostat should do the trick. This would allow the system to detect usage by seeing a significant drop in temperature as the tank refills with cold. Which in turn would determine a pattern of use and possibly how much water has been used. Which could then be used in future witrh smart scheduling to only heat the water required based on average usage.