It's time to admit we have a monster problem. How can you spin a harrowing yarn about a bloodsucking vampire or slavering werewolf, when any grade-schooler could identify the telltale symptoms of an attack and advise you of the proper countermeasures? Our monster-savvy age demands new beasties; here are some possible candidates.
The Inspector lives in the basement. He has a key to your house. He has a key to every house.
The Canker is transmitted via airborne spores. Try not to inhale.
Wild animal attacks aren't really a contemporary hazard, but our streets are full of marauding vehicles. I played around a bit with beast-shaped machines, but then decided that a machine masquerading as a person was more interesting. The Junk-Man roams the streets, wrapped in a shabby raincoat, looking for unwary pedestrians to trample.