"alerter" in the adjective sense
1. alert, watchful
engaged in or accustomed to close observation
"caught by a couple of alert cops"
"alert enough to spot the opportunity when it came"
"constantly alert and vigilant, like a sentinel on duty"
2. alert, brisk, lively, merry, rattling, snappy, spanking, zippy
quick and energetic
"a brisk walk in the park"
"a lively gait"
"a merry chase"
"traveling at a rattling rate"
"a snappy pace"
"a spanking breeze"
3. alert, alive, awake
mentally perceptive and responsive
"an alert mind"
"alert to the problems"
"alive to what is going on"
"awake to the dangers of her situation"
"was now awake to the reality of his predicament"
Source: WordNet® (An amazing lexical database of English)
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