How to run a macro when certain cells change in Excel

macro.vb

Private Sub Worksheet_Change(ByVal Target As Range)
    Dim KeyCells As Range

    ' The variable KeyCells contains the cells that will
    ' cause an alert when they are changed.
    Set KeyCells = Range("A1:C10")
    
    If Not Application.Intersect(KeyCells, Range(Target.Address)) _
           Is Nothing Then

        ' Display a message when one of the designated cells has been 
        ' changed.
        ' Place your code here.
        MsgBox "Cell " & Target.Address & " has changed."
       
    End If
End Sub