Form 4 is the SEC filing that discloses insider transactions — purchases, sales, and option exercises by officers, directors, and 10%+ owners. It lands within two business days of the trade, which makes it the closest thing to real-time insider intelligence.
Most Form 4s are noise: scheduled 10b5-1 plan sales, tax withholding, or option exercises with immediate sells. The ones that matter are open-market purchases, especially by the CEO or CFO, and large sales outside a pre-existing plan.
The fields that matter
Transaction code: P = open-market purchase, S = open-market sale, M = option exercise, A = grant, F = tax withholding. Only P and S tell you what the insider actually chose to do.
Transaction type: D = disposed, A = acquired. A disposal after an acquisition (M followed by S) is usually mechanical. A straight disposal (S with no M) is a choice.
Relationship: 'Director', 'Officer', '10% Owner'. The CEO buying $500K in the open market is a signal. A 10% owner selling 2% of their stake after a 400% run is just profit-taking.
Red flags
Cluster sales: three or more insiders selling in the same week, especially after a financing 8-K, means they know something you don't.
Zero open-market buys across the entire C-suite for 12+ months while the company burns cash. If management won't buy the stock at $0.50, why would you?
Options exercised and held (M, no S) can be bullish — the insider is taking the tax hit to own the shares outright. Options exercised and immediately sold (M + F or M + S) is just comp.
How to track them
EDGAR search: issuer = company ticker, filing = 4. Most 10-K/10-Q footnotes also aggregate insider holdings in the 'Beneficial Ownership' table — compare quarter-over-quarter.
On Stocks Leak, every ticker page surfaces the last 90 days of insider Form 4 activity with buy/sell tags and running totals.