I am rebooting my original Ripleys Watch thread below with the accumulated information plus some extra pics.
Hi guys,
I tried a quick search for the appropriate keywords "Seiko" & "Speedtimer" and found nothing so hopefully this is new information.
I stumbled onto the following website http://watchesinmovies.info following links related to a watch for a different costume.
So while there I decided to see if they had the Pulsemeter listed for the Colonial Marines and they don't but they do have the following information about Ripleys wristwatch including a few screenshots.
Aliens (1986)
Character: Ripley
Actor: Sigourney Weaver
Watch: Early 1980′s Seiko Speedtimer 7A28-7000
Apparently this watch was designed by the same person as the watch worn by Bishop shown below.
Hope this helps someone.