Notification Limitation?

Notifications will only fire when a data entry type (Quickbase calls these "Scalar") field is changed.  So for example if a record becomes overdue at midnight tonight that will not trigger a flurry of notifications that some task on a project is overdue. 

You have two options. One is to create a subscription report which you would receive every morning of inventory which is low. That is actually what I recommend. 

If you actually want to know the second that inventory becomes low then you would have to set the notification up to fire when the employee record is changed. You would need to look up any totals you need from the parent inventory and trigger off that employee record being changed because that is where the data entry is happening.