Reflex

The Reflex (RDS) is an American red dot sight.

It is an available attachment in Battlefield 3 and Battlefield 4.

Battlefield 3
"American made Red Dot Sight for extremely fast and clear target acquisition in close quarters. The single Red Dot in this sight makes getting on target easy."

- Battlelog discription

The Reflex (RDS) appears as an attachment in Battlefield 3. It is the standard red dot sight for US and European weapons, as the Kobra is for Russian and Chinese weapons. Functionally the two sights are identical, and can be unlocked for the opposite faction's weapons when all the faction default attachments have been unlocked for a weapon.

Battlefield 4
The Reflex (RDS) was first seen in the Battlefield 4: "Angry Sea" E3 2013 Gameplay Trailer, attached to Recker's Saiga 12K alongside a magnification sight.

Trivia

 * The Reflex in Battlefield 3 is referred in the game files as the RX01, a real life optical sight that it is based on.