Don't let the name fool you. They may be commonly referred to as "drones" but they don't have to make a constant noise. As they descend from the sky, you'd probably never hear them coming. An assistant professor of aerospace engineering told Gizmodo that, "fixed-wing powered gliders, or rotorcraft in near free fall, can be as silent as a thief in the night ... This point is relevant for those who hope to detect drones by their acoustic signature, including the Secret Service guarding the White House."
Oh, and small drones have been developed that mimic insect and bird movements, making it possible for them to travel virtually undetected into urban areas. Sleep tight.
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