Olfactory sensor
From Tardis Wiki, the free Doctor Who reference
Olfactory sensors provided robots with a sense of smell. K9 Mark IV once used this to track down a pair of Slitheen. (TV: The Gift) K9 Mark 2 used his sensors when he was temporaily blinded, to track Trojan's foul breath to aim his photon beam at the creature. (TV: The Eclipse of the Korven)
