For the convenience of our guests and us, we installed a keyless door lock for both our apartments. When our guests book we ask them if they'd like to provide us with a 4 digit code of their choosing or if they want us to pick a random code. We can program the code for the dates of their stay with their code from an app on our phone. I try to send our guests a picture of the door to their apartment along with a confirmation that their code is ready for their arrival the day before they arrive. And after they leave, we delete the code. It's so nice not to worry about keys and makes is seamless for last minute guests.