¿Por qué la alarma?
Normally, feminine words that start with the letter a take el rather than la so as to avoid the effort in pronouncing two adjacent as. El agua etc.
Why then is does alarma take a la?
1 Answer
It's because the emphasis is not on the first syllable. The rule is to use el when the word starts with an accented 'A' (that is, when the first syllable is the sílaba tónica; it doesn't have to have a written accent above it).