Regardless of how you mean this word, it would be the same word
for both watchers and watchmen.
watchers as in television watchers = מביתים (mabitim)
watchers as in guards = שומרים (shomreem)
watchers as in spectators or scouts (also TV watchers) = צופים
(tsofim)
watchers as in observers (scientific or otherwise) = משקיפים
(mashkifim)