A portable timepiece

wrist watch, pocket watch, hunter, half-hunter, stopwatch, chronometer, digital watch, analog watch, ticker*; see also clock.

Strict attention

lookout, observation, observance, surveillance, awareness, attention, vigilance, guard, heed, watchfulness.

Antonyms neglect*, sleepiness*, apathy. *

A period of duty or vigilance

patrol, guard duty, night watch, shift, vigil, picket duty, sentry duty, trick*, dogwatch*, graveyard watch*, graveyard shift. *

Those who keep a watch, sense 3

guard, sentry, sentinel, picket, watchman, lookout, scout, spotter, observer, signalman, flagman, shore patrol, S.P., military police, M.P.; see also guardian 1.

To be attentive

observe, see, scrutinize, follow, attend, mark, regard, listen, wait, attend, take notice, contemplate, mind, view, pay attention, concentrate, look closely.

To guard

keep an eye on, keep (a) prisoner, patrol, picket, police; see also guard 2.