Alertly
/əˈlɜːrtli/
Definition 1 of 1
Pro Tip 1/3Active Awareness
Used when someone is actively paying attention and prepared to react quickly. 
The guards stood alertly at the museum entrance, aware of every visitor.
Pro Tip 2/3Sense of Urgency
Suggests a situation that requires immediate attention or swift action. 
The firefighters moved alertly to evacuate the building.
Pro Tip 3/3Observant Behavior
Describes someone who is very observant and notices details that others might miss. 
He walked alertly through the crowded market, spotting potential pickpockets.