I'm actually impressed teams can steal signs even with technology. The catcher and pitcher often vary the important sign in the sequence, which can change with every pitch. Something like "strikes plus one", so on a one strike count, the second sign is the true sign. If another strike is thrown, the third sign becomes the important one and the others are decoys.
And they can change the modifier at any time, to maybe "balls plus two" or whatever. Merely recording it and watching the signs play out is still very difficult to establish what is the actual sign...