diff --git a/NKNU_Classroom_Safety.html b/NKNU_Classroom_Safety.html
index 5595fce5c4..5ed0f70f1e 100644
--- a/NKNU_Classroom_Safety.html
+++ b/NKNU_Classroom_Safety.html
@@ -48,7 +48,6 @@
   var leftbuttom = document.getElementById('leftbottom');
   var rightbuttom = document.getElementById('rightbottom');
   
-  var myTimer;
   var aud = document.getElementById('aud');
   var alarm = new Audio(aud.value);