@ToKiHyou I think we can safely say none of us want that in our house! Can I ask have you set your front door trespassing settings to Disallow Vampires? That's supposed to keep them away. I had one in my Sims home before I realised there was a specific door setting for them and the door was unlocked at the time and they walked in uninvited and started hissing. Scared the very bejeebers out of my Sim ...and me if I'm honest.
Have you had other instances of Sims walking in? I know Vampires are different, but I wonder if it's part of one of the Sims invading homes bugs. There's a link here to the open bug reports:
https://answers.ea.com/t5/Bug-Reports/CURRENT-ISSUE-Sims-invading-Homes/td-p/13285790
