diff --git a/main.lua b/main.lua
index 1f43dd8..74d27ed 100644
--- a/main.lua
+++ b/main.lua
@@ -2,6 +2,19 @@
 local util = require("util")
 local window = require("window")
 local button = require("button")
+
+-- entities that has update method
+active_entities = {}
+
+function register(entity)
+    util.add_entity(active_entities, entity)
+end
+
+function unregister(entity)
+    util.del_entity(active_entities, entity)
+end
+
+--load room list
 local rooms = require("rooms")
 
 current_room = rooms['default']
@@ -114,6 +127,9 @@ function love.load()
 end
 
 function love.update(dt)
+    for i, e in ipairs(active_entities) do
+        e:update(dt)
+    end
 end
 
 mw, mh = 0, 0
@@ -130,13 +146,10 @@ function love.mousepressed(x, y, button)
 end
 
 function love.draw()
-    love.graphics.push()
     love.graphics.translate(mw, mh)
     love.graphics.scale(MULTIPLIER)
 
     screen:draw()
     inventory:draw()
     log:draw()
-
-    love.graphics.pop()
 end
diff --git a/room/keypad.lua b/room/keypad.lua
index c02e6b9..3160fdd 100644
--- a/room/keypad.lua
+++ b/room/keypad.lua
@@ -27,6 +27,8 @@ function m:from(t)
     kp.padx = sx
     kp.pady = sy
     kp.indicator_width = kw
+    kp.state = 'normal'
+    kp.timer = 0
 
     for i = 1, 9 do
         local x = sx + kd * ((i-1)%3)
@@ -53,6 +55,8 @@ function m:from(t)
 
     edge:set(m, "down", kp.room)
 
+    register(kp)
+
     return kp
 end
 
@@ -70,14 +74,36 @@ function m:accept()
     if self.number == self.code then
         log:log("correct!")
     else
+        self.state = 'wrong'
         log:log("it seeems that the number does not match.")
     end
 end
 
+m.update = function(self, dt)
+    if self.state == 'wrong' then
+        self.timer = self.timer + dt
+
+        if self.timer > 1 then
+            self.state = 'normal'
+            self.timer = 0
+            self:clear()
+        end
+    end
+end
+
 m.draw = window.draw(function (self)
     love.graphics.setLineWidth(3)
+
+    -- draw indicator box
     love.graphics.rectangle('line', self.padx, self.pady, self.indicator_width, self.key_size)
-    love.graphics.printf(tostring(self.number), self.padx + 5, self.pady + 5, self.indicator_width - 8, 'right')
+
+    if self.state == 'normal' then
+        love.graphics.printf(tostring(self.number), self.padx + 5, self.pady + 5, self.indicator_width - 8, 'right')
+    elseif self.state == 'wrong' then
+        love.graphics.printf("wrong", self.padx + 5, self.pady + 5, self.indicator_width - 8, 'right')
+    else
+        error("keypad is not in a defined state")
+    end
 
     for i, v in pairs(self.keys) do
         v:draw()
diff --git a/util.lua b/util.lua
index 320e92c..fd49ede 100644
--- a/util.lua
+++ b/util.lua
@@ -27,7 +27,7 @@ function m.add_entity(a, x)
 end
 
 function m.del_entity(a, x)
-    table.remove(a, x)
+    table.remove(a, x.idx)
 
     for i, v in ipairs(a) do
         v.idx = i