Worn by: Will Smith as Robert Neville
Reference: Hamilton Khaki Aviation
Brand: Hamilton
Robert Neville fought terrifying zombies in I Am Legend wearing a customized version of the Khaki Aviation Twilight. The watch was designed to accompany professional pilots through even the most extreme circumstances—appropriate for the last man on Earth battling infected creatures in a post-apocalyptic New York City.

Worn by: Will Smith as Robert Neville
Reference: Victorinox ST-4000
Brand: Victorinox
Verification: 100% - Visual confirmation.
Dr. Robert Neville is a military virologist and the last human survivor in post-apocalyptic New York City after a man-made virus transforms most of humanity into vampire-like creatures called Darkseekers. Immune to the virus, Neville spends three years searching for a cure using his own blood while surviving with his dog Sam. The Victorinox ST-4000 is crucial to his survival - he sets its alarm daily using a Farmer's Almanac to ensure he returns home before sunset when the Darkseekers emerge. Smith's character also wears a second watch, possibly a Hamilton Khaki X-Wind, as a mechanical backup.

Source: https://wornandwound.com/watches-on-the-screen-i-am-legend/