Update: Figured someone would ask, so here's the line from a correction to my currently posting story, Lost With Nothing to Lose:
The doorway darkened long before the hiss of air harkened the pressure equalization between the two ships.
That's... not right. "Harken" means "listen" or "pay attention to", and makes no sense in that context. I think the word you're looking for may be "heralded".
Also, according to Dictionary.com, "harken" is the spelling for the noun, while "hearken" is the spelling for the verb. but generally, the American spelling "harken" is truer to it's etymological roots, while the British "hearken" appears to have been modified to conform to the spelling of "hear" (which is the basis of the word).
"Hearken" comes from Old English heorcnian, "listen", which was related to, but distinct from, hieran, "hear". English underwent a major vowel shift in the meantime, but "hearken" is closer to the original than "harken".
Also, my browser's spellchecker is fine with "hark" and "hearken", but doesn't like "harken". Not that that means much; its dictionary has some weird holes in it.