Seeker Drones were a Furon homing missile launcher weapon for the Saucer. They destroyed ground targets, or took down airborne targets like Nexo Saucers, Helicopters, and Planes. The manual described them as angry hornets. The Seeker Drones were bright and presumably plasma/electricity or an other energy based weapon.
The Upgrades mainly included the amount that were fired simultaneously, ammo capacity, and damage.