Dr Paxton has eschewed sonar detectors, underwater cameras and robot submarines in favour of an entirely different method of detection: statistics.

ECONOMIST: Statistics

Cameras tracked their movements and were used to control a rat-sized robot that shared a cage with the rodent subjects.

BBC: Rats and humans meet via virtual reality and robotics

I.e. the dual-cameras on the HOM-BOT can show you where the robot is, and mapping presents a display of its path through the house.

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Japanese company Sohgo Security Services has developed the "Guardrobo D1, " a meter-tall robot that can patrol offices, homes or stores, watch for trouble using digital cameras and sensors, and alert human guards via radio if it detects a problem.

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