The weapon fired a red heat beam. It was designed for eradicating organic material, so it was of little use against other objects. For example, when the Eradicator was fired upon showman Vorg's miniscope, it had no effect upon it or its occupants.
The Eradicator was made inoperable by Comissioner Kalik by removing a piece from it, in order to lay blame on President Zarb's policies. When Kalik freed the Drashigs, the area was defenceless, but Vorg found the missing piece and repaired the machine in order to kill the Drashigs. (TV: Carnival of Monsters)