no you dont have to open the door, but if they have a warrant they can bust in. i had a friend who had a warrant for his arrest, but was at a different friends house when the police came to the door. the police were like open up we can see you there, all he said was no through the door, because friend x(homeowner isnt home) they couldnt do anything. a couple of wks later though they did catch him in his own house, and busted in his door to get in.