diff --git a/doc/lss.rst b/doc/lss.rst
index 2906e06b..d37e3c0a 100644
--- a/doc/lss.rst
+++ b/doc/lss.rst
@@ -47,6 +47,10 @@ Or, you can run fastscan procedure ::
 
     ret_bool, lss_id_list = network.lss.fast_scan()
 
+.. note::
+   Before you run fastscan, you have to make sure the devices are in non-configured
+   or unconfigured state.
+
 Once one of sensors goes to CONFIGURATION state, you can read the current node id of the LSS slave::
 
     node_id = network.lss.inquire_node_id()