if you are on data entry form, you can trigger the AfterUpdate of that specific field.
private sub yourFieldName_AfterUpdate()
If Me!yourFieldName.Value <> Me!yourFieldName.OldValue And _
Me!yourFieldName.OldValue & "" <> "" then
MsgBox "Status of field has changed from " & Me!yourFieldName.OldValue & _
" to " & Me!yourFieldName.Value
' do the rest of code, or email if you want
End If
End Sub