These alerts report when a stock has an unusually high number of shares on the best bid or ask.  These are very short term alerts aimed at very fast, experienced traders.

We only generate these alerts for stocks with an average daily volume of less than 3,000,000 shares per day.  If a stock typically trades less than 1,000,000 shares per day we require a bid or ask size of 6,000 shares or greater to generate an alert.  Otherwise we require a bid or ask size of 10,000 shares or greater to generate an alert.  We also have additional filters to prevent a stock from reporting this alert too often.  For example, if the best bid for a stock is 20,000 shares at $10.00, then someone adds a bid of 100 shares at 10.01, the 20,000 shares still appear in the order book.  When the 100 shares go away, and the best bid returns to the 20,000 shares at $10.00, we do not report another alert.

If we report a large bid or offer size, then the size grows even larger, we typically report another alert.  The message for that alert is labeled "(Size increasing)".

If a stock is showing a large bid or ask size, and the price changes but the size remains large enough, we may report an additional alert.  The message for that alert is labeled "(Price rising)" or "(Price dropping)".  This message only applies to large size.  For example, if we see a 20,000 shares on the bid at $10.00, we report an alert.  If the best bid changes to 100 shares at $10.05, we report nothing.  If the best bid then changes to 15,000 shares at $10.02, we report a second alert, labeled "(Price rising)".

If a large bid is dropping, or a large ask is rising, this makes for a stronger alert.  If a large bid is rising, or a large ask is dropping, this may be a "head fake"; someone may be trying to trick you by showing large size in one direction, while slowly buying or selling in the other direction.  In either case, we report an alert.

The bid and the ask are two completely separate alerts.  The size or price of the bid does not influence the Large ask size alert.  The size or price of the ask does not influence the Large bid size alert.

More options related to these alerts are listed below.