Often a stock price change can be related to when an executive, board director, or president quickly sell off their current company holdings.
Is there a way of monitoring a company's insiders selling off shares in a timely manner?
Exec Insiders have to file with the SEC and some sites like secform4.com track it. But many insiders have selling programs where the sell the same amount every month or quarter so you would have to do your homework to determine if there are real signals in the activity.
SEC Form 3 and SEC Form 4 are filed when insiders make share/derivatives acquisitions, transfers, sells and buys
There is a time limit AFTER the action where they can be filed, such as 12 business days, so this can be a substantial amount of time after the effect on the market, depending on your strategy.
You can aggregate these forms from SEC sources or from third party websites and services.
In some cases, types of insider trading are permissible at certain intervals, so if you learn about when certain shares become unlocked, you can try to predict what insider actions will be and share price movements around those times.