Luckily for me DS is a well behaved child so never really done reward charts. We do do earning priviledges/ losing them etc.
BUT he has a horrid habit of NEEDING chocolate, drink, batteries in a toy everytime I go to the loo. I have IBS so often it takes me 5 minutes each time.
So AIBU to put a chart on the door in the hope that he'll come to door, open his mouth to demand something and then think better of it because he'll lose a privelidge for doing so?
Bit wary because last time I told DS to disturb me only for death/ hanging off limbs he climbed the worktop himself and had to disturb me as he has a hole in his chin from falling down. 
But I need to go in peace and he needs to learn priorities. 