diff --git a/devices/__init__.py b/devices/__init__.py
index 2aef3b5..d8a79f8 100644
--- a/devices/__init__.py
+++ b/devices/__init__.py
@@ -190,7 +190,7 @@ class base(dict):
         return "default warning text - replace parent warning_text function"
 
     def previous_value(self, key):
-        self.__previous__.get(key)
+        return self.__previous__.get(key)
 
 
 class shelly(base):