Due to the woodpecker biology, they have sensitive smelling, so they don’t like strong odors. In some woodpecker deterrent sprays, manufacturers use smells that repel woodpeckers to keep them out. Also, woodpeckers don’t like gel repellent that doesn’t allow them to make a nest. Ultrasonic sound will also scare them away. We don’t hear it, but for birds, it’s an unpleasant noise.