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All drones except Pulse Drones have a local scanner, which they can use to detect nearby agents, even if they are in soft cover. A drone uses its local scanner to investigate an interest point, or when preparing to hunt.
The scan has a radius of 4 tiles measured by Euclidean distance; it detects agents or a rescued Courier or Prisoner if they are within range. The scan ignores soft cover, but is blocked by tall cover and hard cover.