Find Al Gore hiding behind the tree right beside the cinema and talk to him. He'll add you immediately as a friend and he'll give you this side quest as well. For the first set of tasks, you have to place the sensors on three specific locations marked in your map.
1: Wind Cockerel at the rooftop of the barn.
2: Fire danger meter west of South Park Elementary
3: Electric transformer, in the roof of Kenny's garage.
Report back to Al Gore and you'll receive Al Gore's Storage Key. Go to U-Stor-It and open the storage shed. Talk to him and you'll receive the ManBearPig Defilibrator. Once you have the alien probe tool, head to the sewer and follow the path until you reach a generator right before the turn. Place the defilibrator there then report back to Al Gore to complete the quest.