Gustav Helsing has a powerful artifact called the Cross of the Mayhews which serves to keep vampires out of his home yet previously in the show it had been established that Gustav had no crosses hanging up in his house and this was part of what had lead Max to wrongfully suspect that Gustav was a vampire.
The Cross of the Mayhews, which hangs in Gustav Helsing's house, seems to have an on going inconsistency. Occasionally it'll just drive vampires from the home or force them out with an electrical jolt while in other instances it out right destroys a vampire that enters the house.