A driveway alarm is a device that detects people or vehicles entering a driveway. The alarm can alert residents that someone is approaching their house. Driveway alarms are often integrated with a larger security system that can activate gates, lighting, or cameras when an approaching vehicle is detected. Driveway alarms can be useful on a large, rural property with a long driveway. A homeowner with a car-length driveway may not find the same utility.