Eclipse glasses

Eclipse Glasses are a gadget invented by the Mechanist. They first appeared in The Day of Black Sun, Part 2: The Eclipse.

Overview
Sokka commissioned the Mechanist to produce these special glasses so that when the invasion force invaded the Fire Nation on the Day of Black Sun, they could observe the eclipse safely as a means of keeping track of their time. The Mechanist produced dozens if not hundreds of these glasses for each invasion member. The only ones who didn't wear them were Aang, Sokka, and Toph, who were searching for Fire Lord Ozai in the Fire Nation Capital's underground bunkers. (nick.com)