I need to be able to set a limit on a cell value and be able to warn if
the threshold is about to be breached. For example:

If the maximum limit for a cell is 5,000 and it goes past 5,000, a
warning message would be displayed alerting the limit being surpassed.

The cell is updated from another worksheet, so the value being added
into it is not controlled from this spreadsheet (It's being referenced
in). But, the warning should be seen from either the first spreadsheet
(Where the value is being entered and then referencing the cell in
question in another sheet), or in the spreadsheet where the cell is.
Both would be great, if that's possible. Thank you in advance for
any/all help in this matter.