Automation not triggering on sensor depth change

If you’re looking for a “delta” type trigger (new_value - old_value > some_number) then you’d have to do that with a state trigger and a template condition:

{{ trigger.to_state.state | float(0) - trigger.from_state.state | float(0) > 0.5 }}

I’d also recommend avoiding device triggers entirely; here’s a link to a good post showing why.