If you consume 100watts, reset a countdown timer. So as home assistant polls the outlet, it should keep resetting the timer. If the timer expires, then notify that the dryer is done.
But I suppose the countdown approach would still trigger the same thing. I suppose if I didn't really want the extra alerts I should be monitoring the duration of power consumption and exclude the ones that are of a shorter duration.
I might try the countdown approach for something different and see what results I get. Thanks for the idea!
I was thinking of doing something similar to what you are dong but was trying to think of how to do it without the custom virtual device.
They don't even cost that much compared to ones that aren't connected.
And it ended up being a fun project for me ^.^