To all landlords: My tenant leaves her ac unit on when she is home absent (8-10 hours).?

As far as I know, no electrical devices should be left on in a house when people are not there. Chances of short circuits because of overheating resulting in fire are real and many fires have occurred due to ac units mailfailure. In other words, she is putting in danger my house and my life since I live in the second floor. I already left her a note explaining why she cant leave it on and she does not pay attention to me and keeps on doing it. What should I do?