Amazon issued patent for delivery drones that can react to screaming, flailing arms
https://www.washingtonpost.com/news/the-switch/wp/2018/03/22/amazon-issued-patent-for-delivery-drones-that-can-react-to-screaming-flailing-arms/
An array of onboard sensors could detect whether humans are welcoming Amazon's delivery drones in or shooing them away.