Dim mRg As Range
Dim mStr As String

Private Sub Worksheet_BeforeDoubleClick(ByVal Target As Range, Cancel As Boolean)
If Not Intersect(Range("A1:C7"), Target) Is Nothing Then
    Set mRg = Target.Item(1)
    mStr = mRg.Value
End If
End Sub
Private Sub Worksheet_Change(ByVal Target As Range)
    Dim xRg As Range
    On Error Resume Next
    Set xRg = Intersect(Range("A1:C7"), Target)
    If xRg Is Nothing Then Exit Sub
    Target.Worksheet.Unprotect Password:="123"
    If xRg.Value <> mStr Then xRg.Locked = True
    Target.Worksheet.Protect Password:="123"
End Sub
Private Sub Worksheet_SelectionChange(ByVal Target As Range)
If Not Intersect(Range("A1:C7"), Target) Is Nothing Then
    Set mRg = Target.Item(1)
     mStr = mRg.Value
End If
End Sub