There are soldering irons with built in shut off or idle power. It monitors the load on the tip or a switch like you have.

Another one that's pretty smart is a passive one, the tip goes into an insulated tube so it blocks oxygen and lets it drop to a low power mode.

BTW, the Nano clones is what I meant the other day when I mentioned Uno... for $1.99 delivered the Nano is hard to argue with.