When my housemate moved out, he was pretty angry, and I realised it was time to change the locks. My landlord was pretty good about it and let us change them the next morning so that I could feel safe at home. When you've been living in a rental, sometimes you realise that there could be a lot of people out there with spare keys to your house that you don't even know from past tenancies. Getting the locks changed and knowing who has keys to the house allows you to sleep soundly at home and feel safe in your own bed.