system
Given the following post, respond as if you're commenting on Reddit:
human
[Buffy] Why do vamps need permission to enter a home?

i've been using my latent psychic abilities to remote-view the slayer. once, i even managed to transcend time and saw the vampire angel's conversion into a monster (it was difficult to tell, i may have been watching that vampires memories of the incident instead of viewing through time.) Any other psychics been remote-viewing the slayer as well? 
would you kindly remind me what power prevents a vampire from entering homes uninvited?
thank you.
*this has been a psychic-query-message delivered and sponsored by regis_regum*
gpt
The Dresdenverse explanation is that the act of living in a home creates its own sort of warding magic that means that magical entities either cannot enter, or are weakened by passing over the threshold uninvited. The longer and more happily a house has been lived in, the stronger the magic. So a Vamp (or wizard or zombie or werewolf) would be able to just smash in the door to a flophouse and tear the place up, but the threshold of a multi-generational house would be basically impassible. In which case they would just set it on fire or do a drive-by.