Eagle Vision

Eagle Vision is a first-person view in Assassin's Creed. It changes the camera's point of view to that of Altaïr. It also uses different color glows to distinguish for the player between different classes of NPCs:

To use Eagle Vision, the player must press the Head button. Depending on control settings, the Head button will most likely be either (Playstation 3), Y (Xbox 360), or E (PC default layout). In addition, the Synchronization bar must be at its current maximum capacity, otherwise pressing the Head button will instead result in a first-person view with no extra benefits.

When Altaïr climbs to the top of a View Point, he must press the Head button to view his surroundings and update the map.

In Assassin's Creed II, Ezio can also use the Eagle Vision like his ancestor. However, he can move while using his power unlike Altaïr who needed to stay still (even if the glows remained on the people for some time). The HUD disappears while using it though, and it will be a third-person view.

At the end of Assassin's Creed, after Altaïr (controlled by Desmond) kills Al Mualim, Desmond gains the ability to use Eagle Vision outside of the Animus. This allows him to read hidden messages all over the Abstergo lab. In addition, Lucy glows blue, confirming her as an ally.