You can use publicly available data feeds that changes every few minutes. For example, CNN's Afterhours trading data [0] seems to work pretty well. And it's jus

You can use publicly available data feeds that changes every few minutes. For example, CNN's Afterhours trading data [0] seems to work pretty well. And it's just HTML, so you just hash it and you're good. [0] http://money.cnn.com/data/afterhours/ http://money.cnn.com/data/afterhours/