A CILAS DHY 307 laser designator, as used in the film, but without the tripod.
A laser is a type of weapon, one that the aliens did not have.
Laser designator[]
A laser designator is a laser light source which is used to designate a target. Laser designators provide targeting for laser guided bombs, missiles, or precision artillery munitions, such as the Paveway series of bombs, Lockheed-Martin's Hellfire, or the Copperhead round, respectively.
Battle of Los Angeles[]
During the Battle of Los Angeles, humans use a Northrop Grumman Laser Systems AN/PEQ-1A Special Operations Forces Laser Acquistion Marker (SOFLAM) to lase a priority target , which is eventually destroyed by the second missile impact. Its destruction instantely starts to shut off all comms with the alien Wedge Ship drones, which fall out of the sky, regardless if they were engaging a target, performing ELINT, loitering, or in a saucer formation.