Depends on the following word beginning with a vowel or not, yes. I have trouble imagining a context in which the word immediately following "tire-bouchons" is not a verb (e.g. Ces tire-bouchons sont cassés"), or where the verb marking it as plural doesn't show up in the sentence somewhere (e.g. "Ils sont cassés, ces tire-bouchons").

p.s. Daniel, what's your problem with calling it a "pull-plug", hm?