Don't know which should win; they both have three questions.
I lean toward the singular.
Moved alarms to alarm. Vote on synonym here: https://android.stackexchange.com/tags/alarm/synonyms
Isn't the rule of thumb that tags should be plural? Wikipedia uses that method:
Set categories are named after a class (usually in the plural).
Eg, if we're talking about "New York City" the tag is not "city" but "cities" -- because the tag would be applied to "Paris", "Chicago" etc.
Just so for "apps" "alarms" "keyboards" etc.
I may have followed this rule inconsistently, myself. Mea Culpa.