What is a cluster alert?
A cluster alert fires when several different insiders at the same company independently buy (or independently sell) within a short window of each other. It's not a property of any single Form 4 filing — it's a pattern InsiderTradingRadar detects across multiple separate filings from different people.
The exact rule
A cluster is 3 or more distinct insiders at the same company, trading the same direction (all buying, or all selling), within a 5-calendar-day window. Only genuine discretionary open-market trades count toward this — the same open-market buy/sell classification used everywhere else on this site, which already excludes compensation awards, tax withholding, gifts, and other mechanical activity. Scheduled Rule 10b5-1 plan trades are excluded too: 3 insiders whose pre-scheduled plans happen to execute in the same week isn't a cluster, it's 3 calendars lining up.
Why this is treated as a stronger signal
One insider's trade can have all kinds of ordinary, non-predictive explanations — a personal liquidity need, portfolio rebalancing, tax planning. Those explanations get harder to sustain when several people at the same company, who don't necessarily coordinate with each other, independently make the same discretionary call within days of one another. It doesn't guarantee anything about what happens next — see the track record for how cluster signals have actually performed, sample sizes included — but it's a meaningfully different situation than a single trade in isolation.
How it shows up in your alerts
A cluster alert is separate from your regular per-filing alerts and isn't affected by your rule's category excludes or minimum dollar value — those filters apply to individual filings, not the cluster pattern itself. Every cluster alert links back to each constituent Form 4 filing that makes it up, so you can verify the underlying trades yourself rather than trusting a summary.