Calls at unreasonable hours stand a good chance at coming from overseas, where it's within business hours. Seldom will the caller have anything to say as it's often a computer doing it. It may be safe to say they're looking for numbers they can count on to be answered at all times, too. Telepests probably have enough of an idea that calls during night hours most often are emergencies, but instead, they're using it as a way to test how often your number's answered by a live voice. Dash their hopes by not taking unknown numbers either manually or automatically.