Two ad agencies in Brazil built this billboard in Rio de Janeiro as a way to kill mosquitoes that carry the Zika virus. It emits Lurex 3, a chemical that smells like human sweat. This attracks mosquitoes. It traps the bugs inside, killing them by dehyrdration. Hack A Day explains:
Inside the billboard are canisters of Lurex 3, a lactic acid-based mosquito attractant that is available pretty cheaply on Amazon. The lactic acid mimics the scent of human sweat and is released outward to distances up to 4km (2.5 miles) in a fine mist along with CO₂. Together, the Lurex and CO₂ act like a sweaty, mouth-breathing human beacon to lure mosquitoes into the billboard, where they become trapped and are doomed to die of dehydration.
The creators have made the plans available for free, so anyone with the resources can build one.