Late as fuck response, but it's all over. Sentiment analysis on SEC filings, scanning financial reports.
The key is to do this automatically. The firm I work at, because noone can find me here, is Citadel, I'm an intern there right now.
There's a lot of focus on deploying HFT strategies (most of our strategies) in black boxes right next to the exchanges. This why our order gets on the fiber line straight to wallstreet as fast as possible.
Some of our strategies simply rely on picking off bad trades. Some retail guy selling at 4 cents below current ask? Buy all as long as downward momentum is over such and such limit. You see all the extra tiny "vibration" on certain stocks like microsoft? That's us or another big firm (Citadel is far from the biggest) just edging based on momentum models that act on the milisecond level.
Algo trading isn't hard, go on quantopian and download the hundreds of algos people host on there and play around.
If you want to do it professionally it's a different ball game. If you're not from an ivy or getting stats, CS, or math degree from a top school you're wasting your time.
If you are the above I highly recommend this field. Citadel, Bridgewater, KCG, Jump, or Tower Research pay a fucking shitton.
To give you an idea, as an intern I get paid 10k a month plus a housing stipend. Fucking delicious.
As a entry level quant researcher you can expected 110k-140k plus 150%-200% bonus on salary.
Quant traders basically the same base pay with 250%-400% bonus on salary.
Other firms pay a little less, but I know we've lost talent to a few other firms like Tower and a local company called 3Red here in Chicago. Although this is likely because the culture here is fucking cancer and it kills you inside every day