Private Sub Worksheet_SelectionChange(ByVal Target As Range)
Dim Plage As Range
If Target.Cells.Count > 1 Then MsgBox "Sélectionnez une seule cellule.": Exit Sub
Set Plage = Range("B5:E20")
If Application.Intersect(Target, Plage) Is Nothing Then
MsgBox "Hors cible."
Else
MsgBox "Dans la cible."
End If
End Sub