There's actually a useful Zapier script that already does this [0]. I remember reading about it on Mike Knoop's (Zapier cofounder) blog [1]. I haven't tried it out but you should be able to hook it up to any of the alert services that Zapier integrates with. (Which is a lot!)

[0] https://zapier.com/zapbook/webhook/rss/8249/hacker-news-ment...

[1] http://mikeknoop.com/my-zaps/