The most common and most likely answer to this crossword clue is the 4 plus 6 letter word TIME SIGNAL
I've seen this crossword clue in The Daily Telegraph
T
I
M
E
S
I
G
N
A
L
More clues leading to the result TIME SIGNAL
- Backward-looking archbishop is issue for TV announcement
- I'm stealing misplaced report of the enemy's progress?
- Model has drunk a gin with lime – swallowing small pips, perhaps
- Oddly GIs eat lemons regularly, without one getting
- Reverse network grids oddly broadcast beeps, perhaps
- I’m stealing makeup for Pip
- I am silent, nodding ultimately? Wrong — alert!
- Send back impressive pips?
- Radio announcement of how the enemy is advancing?
Buddy explains!
The straight part
We know that "alert" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case alert = time signal.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.