How do rattlesnake detect your presence?

Rattlesnakes don't have eyesight that is great, but they can see and detect movement. They can certainly feel the vibrations of your movements through the ground and taste you on the air with their tongue. In addition, they can sense you via infrared (heat) detecting organs located in pits in front of their eyes. (The rattlesnake is a pit viper, and it gets that name from the "pits" which are the openings to the heat sensing organs.) A link is provided to a picture of a pit viper on Wikipedia. The pits are clearly visible.