Recently I spent two weeks in a hotel in Beijing. I needed an adaptor to get power supply for my laptop from the mains. I was given an adaptor, but was asked to leave 100 Yuan as a  refundable deposit . Interestingly, the number on the currency note was noted down and that very note kept with the details of my room. Two weeks later when I returned the adaptor, I was returned the currency note I had given previously .