The most common and most likely answer to this crossword clue is the 6 letter word BUGLES
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More clues leading to the result BUGLES
Buddy explains!

The straight part
We know that "Calls to wake up" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case calls to wake up = bugles.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.
What does BUGLES mean?
BUGLES noun- A horn used by hunters.
- A simple brass instrument consisting of a horn with no valves, playing only pitches in its harmonic series
- A plant in the family Lamiaceae grown as a ground cover, Ajuga reptans, and other plants in the genus Ajuga.
- Anything shaped like a bugle, round or conical and having a bell on one end.
- To announce, sing, or cry in the manner of a musical bugle
- A tubular glass or plastic bead sewn onto clothes as a decorative trim
- A sort of wild ox; a buffalo.