Spike in electrical consumption
Whenever I see a 3x jump in a power bill for an unoccupied house, my first suspicion is that someone is tapping into your house for free (to them) power because they know you are not home. I had a neighbor in Seattle who did this; went to Alaska every summer to mine gold, spent the winters in Seattle working on fishing vessel repair. One summer an RV parked in his driveway while he was gone and I met the owner, who said he was a relative. The relative left at the end of August and when my neighbor returned in September, he saw the huge power bill. He asked me if I had seen anything, I told him about his "relative", it was phony. From that point on he gave me his contact information in Alaska...