Synonyms for Alertness (same or very similar meaning)
WordNet sense 1 (a state of readiness to respond):
alertingWordNet sense 2 (the process of paying close and continuous attention):
vigilance, wakefulness, watchfulnessWordNet sense 3 (lively attentiveness):
sharp-sightedness, on the qui viveFrom the ODE community, based on WordNetadd/edit