Final answer:
The participle in the sentence is 'annoying,' and it modifies the noun 'alarm.'
Step-by-step explanation:
In the sentence, 'I turned off the annoying alarm and quickly fell back to sleep,' the participle is 'annoying.' A participle is a verb form that can function as an adjective. Here, 'annoying' describes the noun 'alarm.'
Learn more about Participles in English grammar