Lensors are the “bloodhounds” of the Necromongers. Lensors lack free will entirely. They are controlled by a viewscreen device wired into their backs.
The Lensors were Necromonger troops who had lost their faces, or parts thereof, in battle, but who through the application of medical technology remained salvageable. Oftentimes functioning without eyes and ears, their mouths replaced by injectors, even their noses blasted away, they had been converted into tracking devices whose melding of human biology and electronic enhancements that could not be equaled by any tracking device or organism that was either purely organic or wholly mechanical.
The Lensors' most basic ability is to use the titular lens on their faces to detect thermal heat and detect it through heavy material such as heavy armor and buildings (up to being able to see all living beings in a city block instantly). However, they have many other uses. For example, they can detect the changes in the elemental and molecular makeup of the air. They can also discern sounds quieter than any human being and many animals could sense. They can use their abilities to such an acuteness that they can hear a heart beat slower or faster, can detect exhaling or inhaling by the change of carbon dioxide it creates in the air, and can sense organisms hiding in mountain ranges multiple kilometers away. Lensors are fragile beings, however, and in combat they are easily killed and have no way of defending themselves as shown on the Basilica when one is strangled to death by Riddick.