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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"
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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"
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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"