Alertly interested Crossword Clue

 The answer to the crossword clue "Alertly interested" is KEEN.

The word "keen" can mean "having or showing a strong interest or enthusiasm". It can also mean "sharp or piercing". In the context of the crossword clue, it is the first meaning that is intended. So, a person who is "alertly interested" is someone who is paying close attention to something and is very interested in it.

Here are some other words that could be used to describe someone who is alertly interested:

Curious

Eager

Inquisitive

Observant

Vigilant

Watchful

I hope this helps! Let me know if you have any other questions.