watcher

a fire watcher; a China watcher.

bird watchers on the alert for a rare species.

the keen-sighted watcher may catch a glimpse.

"The robber broke into the bank at the storm night, gambling on the fact the night watchers wouldn't find it because of the thunder and lightning."

But besides the meanderings of the Dow and S&P some market watchers have been eyeing volume numbers which have been pretty piddling lately.

avid watcher of sports

casual watcher of movies

watcher of the skies

silent watcher in the corner

active watcher in the discussion

loyal watcher of the TV series