Guessing by the label on the side of it, I'd say it's an Eotech.
L-3 EOTech Holographic Weapons Systems
They tend to go through batteries more quickly than tube style red dots, like the Aimpoints. The Aimpoint is also much more water resistant than the Eotech.
Some prefer the open, heads up style of the Eotech, but I'm not a huge fan of them. They're expensive for what you get.