A wake-up call for team dumped by Alma Mater (5)

I believe the answer is:

alarm

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'mater' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for alarm that I've seen before include "A rousing sound in the morning" , "Wake-up call?" , "Strike fear" , "Frighten, warning" , "Warning bell" .)

I've seen this clue in The Irish Times.

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