Product review (5 stars): Perfect way to know!
This item was perfect for my house! So often my room mates would run the dishwasher, and later that day I would come home and put a dirty dish in their because I didn't know. But with this it's so easy just to flip it over so everyone in the house knows the dishes are clean or dirty.

That is, if everyone remembers to change is when they load or unload the dishwasher...

Oh, and our dishwasher is plastic, so we just put this on the fridge.