How do I ensure that my family's house won't get broken into?

I'm an idiot. Some relatives are letting my friend and I stay at their house while we're on a trip visiting their city. My relatives will be gone the whole time while we're staying at their house. A random guy knocked on the door today and asked if my "dad" was there (he assumed I lived... show more I'm an idiot. Some relatives are letting my friend and I stay at their house while we're on a trip visiting their city. My relatives will be gone the whole time while we're staying at their house.
A random guy knocked on the door today and asked if my "dad" was there (he assumed I lived there). Without thinking, I said, "Oh, you mean Mr. [insert last name]? They'll be out of town until the 26th." The guy was like, "oh really? Okay." And he left. He was driving a truck with lawn mowing equipment. So I could ASSUME that it was just a guy trying to get us to pay him for mowing the lawn.
I feel stupid for saying TO A STRANGER that no one would be home for multiple days. The house is in a nice neighborhood (pro: it's safe, con: it would be a good place to rob). Is there any way to ensure that the family's house is safe? Should I tell my relatives what happened or just hope for the best?
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