Scary ghost story that really happened!!!

Ok, so my parents said last night that they would go shopping for fifteen to twenty minutes. I was in my room blasting Korn reading a book, my brother was in his room and my little sister was out in the hallway with her French horn. (???)
Anyway, I heard this guy yelling across the house, and Betsy my dog barked twice and was silent. If there was really someone there or even if she had thought there was she would have kept barking. I asked my brother if he had said something. He said no so I dismissed it. Then I added up the events in my head and it didn't make sense so I rushed over to the main door. It was unlocked, and it wasn't because Mom and Dad were home. Muttering "shit" I locked the door and got into my defensive position, ready to beat the crap out of whoever came in our house. Satisfied I went back to my room and blasted Korn again. Then I heard a "beep beep beep", the exact same one the door makes when it opens. I ran out into the kitchen and looked around, but all the doors were locked. And Mom and Dad still weren't home.
Freaky, huh? What's your guys' theory on what happened? I honestly think it's the Angel of Death come for my dog who has been alive my entire life. I'm not sure we're going to come home and find her alive.

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