Collecting three alien devices, then activating the Countermeasure Device underneath Corny Complex is the last of Week 12's legendary quests in Fortnite Chapter 2 Season 7. Remember - you only have a week to complete this quest!
This quest set begins with you receiving instructions from one of the payphones located on the Fortnite map, crafting weapons using Alien Nanites, destroying target dummies with IO weapons, searching for books on explosions and deploying scanners in the alien biomes.
Completing this challenge will reward you with 30k XP, which will help you unlock more Battle Stars for the Season 7 battle pass. This will also begin you to the end of this set of legendary quests!
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Note this particular challenge is no longer able to be completed. What's new? Chapter 4 Season 2 has arrived! New additions include the Grind Rails and Kinetic Blades, along with the new Battle Pass, character collection and Eren Jaeger skin. It's a good idea to know how to get XP fast in Fortnite.
Alien device locations in Fortnite explained
You need to collect the three alien devices if you want to activate the Countermeasure Device for this Fortnite legendary quest.
Handily there are three dotted about the Fortnite map, with the first being located just south of Corny Complex on the other side of the river.
You can find the second alien device on the eastern side of the central alien biome - it lies roughly halfway between the biome and the nearest eastern abandoned settlement.
The third and final alien device is located near Scenic Spot, which itself is located north of Corny Complex. If you're having trouble finding this alien device, head down to the road next to this landmark and you'll be sure to spot it!
How to activate the Countermeasure Device underneath Corny Complex in Fortnite
Activating the Countermeasure Device in Fortnite is pretty easy, the problem, however, is that it's located in the IO base beneath Corny Complex. This means you'll have to either fight, avoid or simply run past some powerful NPCs to complete this challenge.
It's a good idea to stock up shield potions, health restores and grab a good weapon or two before heading into the IO base, so you can defend yourself against both the NPCs and any other players.
You can enter the IO base by either using the stairs in the central barn, going through the door located in the cliffside near said barn or using the porta-pottie located in the Corny Complex farmhouse.
Once you're inside the base, you need to head to the room in the bottom left-hand corner on the lowest floor. Here you'll find the Countermeasure Device and, to complete the challenge, all you have to do is interact with it.