I'm using the power monitoring feature on a "heavy duty" z-wave power switch (zooz zen-15) to track the power usage. When it jumps over a threshold for at least a couple seconds, I assume the appliance is on, and then when it drops to zero for at least a couple seconds, I assume it's "done".

Same goes for the kitty litter box, although that's just a standard z-wave power switch, not a "heavy-duty" one. That one gets some false positives, so our counter gets a bit higher than the real one, but the discrepancy isn't a huge deal. Looking forward to debugging this one eventually.