diff --git a/entity.lua b/entity.lua
index f8c9fbc..945d934 100644
--- a/entity.lua
+++ b/entity.lua
@@ -11,15 +11,13 @@ local m = {
 
 m.__index = m
 
-function m:new()
-    local t = {}
+function m:from(t)
     t.__index = t
     return setmetatable(t, self)
 end
 
-function m:from(t)
-    t.__index = t
-    return setmetatable(t, self)
+function m:new()
+    return self:from({})
 end
 
 function m:setpos(x, y)
@@ -50,7 +48,7 @@ end
 function m:draw_lines(lines)
     love.graphics.push('all')
     love.graphics.translate(self.x, self.y)
-    love.graphics.setLineWidth(3)
+    love.graphics.setLineWidth(2)
 
     if type(lines[1]) == 'string' then
         draw_line(lines)
diff --git a/main.lua b/main.lua
index 74d27ed..c8d0553 100644
--- a/main.lua
+++ b/main.lua
@@ -51,7 +51,15 @@ inventory = {
     items = {},
 }
 
-inventory.mousepressed = window.propagate{'items'}
+inventory.mousepressed = window.mousepressed(function (self, x, y, button)
+    for i, v in ipairs(self.items) do
+        if v:mousepressed(x, y, button) then
+            return true
+        end
+    end
+
+    inventory.selected_item = nil
+end)
 
 inventory.draw = window.draw(function (self)
     for i, item in pairs(self.items) do
@@ -65,15 +73,31 @@ inventory.draw = window.draw(function (self)
     window.draw_border(self.width, self.height)
 end)
 
-function inventory:pickup(item)
-    util.add_entity(self.items, item)
-
-    local x = (#self.items - 1) * 60 + (60 - item.width) / 2
+function inventory:set_pos(idx, item)
+    local x = (idx - 1) * 60 + (60 - item.width) / 2
     local y = (60 - item.height) / 2
 
     item:setpos(x, y)
 end
 
+function inventory:pickup(item)
+    util.add_entity(self.items, item)
+    self:set_pos(item.idx, item)
+end
+
+function inventory:drop(item)
+    util.del_entity(self.items, item)
+
+    for i, v in ipairs(self.items) do
+        self:set_pos(i, v)
+    end
+end
+
+function inventory:use()
+    self:drop(self.selected_item)
+    self.selected_item = nil
+end
+
 log = {
     x = inventory.width , y = 0,
     width = WIDTH - screen.width,
diff --git a/obj/door.lua b/obj/door.lua
index 53d8c97..a37b723 100644
--- a/obj/door.lua
+++ b/obj/door.lua
@@ -33,6 +33,8 @@ m.mousepressed = window.mousepressed(function (self)
         if i and i.code then
             if i.code == self.code then
                 self.locked = false
+                inventory:use()
+                
                 log:log("Door opened.")
             else
                 log:log("This seems not a matching key.")
diff --git a/room.lua b/room.lua
index 2c5686f..6ee72d9 100644
--- a/room.lua
+++ b/room.lua
@@ -1,3 +1,4 @@
+local util = require('util')
 local window = require('window')
 local entity = require('entity')
 
@@ -7,13 +8,12 @@ local entity = require('entity')
 -- - edges
 local room = entity:from{
     background = love.graphics.newImage("res/defaultbg.png"),
-    edges = {},
-    objects = {},
 }
 
-local oldnew = room.new
-function room:new()
-    local r = oldnew(room)
+local from = room.from
+function room:from(t)
+    local r = from(self, t)
+    
     r.edges = {}
     r.objects = {}
 
@@ -21,16 +21,11 @@ function room:new()
 end
 
 function room:insert(obj)
-    table.insert(self.objects, obj)
-    obj.idx = #self.objects
+    util.add_entity(self.objects, obj)
 end
 
 function room:remove(obj)
-    table.remove(self.objects, obj.idx)
-
-    for i, v in ipairs(self.objects) do
-        v.idx = i
-    end
+    util.del_entity(self.objects, obj)
 end
 
 room.mousepressed = window.propagate{'edges', 'objects'}
@@ -47,4 +42,11 @@ function room:draw()
     end
 end
 
+function room.calc_align(width, height)
+    local sx = (320 - width)/2
+    local sy = (240 - height)/2
+
+    return sx, sy
+end
+
 return room
diff --git a/room/keypad.lua b/room/keypad.lua
index 3160fdd..c9681ac 100644
--- a/room/keypad.lua
+++ b/room/keypad.lua
@@ -11,22 +11,22 @@ local m = room:from{
 
 local oldfrom = m.from
 function m:from(t)
-    local kp = oldfrom(m, t)
+    local kp = oldfrom(self, t)
 
-    local ks = self.key_size
-    local kg = self.key_gap
+    local ks = kp.key_size
+    local kg = kp.key_gap
 
     local kd = ks + kg
     local kw = kd*3 - kg
     local kh = kd*5 - kg
-    local sx = (320 - kw)/2
-    local sy = (240 - kh)/2
+    local sx, sy = room.calc_align(kw, kh)
 
     kp.number = 0
     kp.keys = {}
-    kp.padx = sx
-    kp.pady = sy
-    kp.indicator_width = kw
+    kp.pad_width = kw
+    kp.pad_height = kh
+    kp.pad_x = sx
+    kp.pad_y = sy
     kp.state = 'normal'
     kp.timer = 0
 
@@ -47,13 +47,13 @@ function m:from(t)
 
     kp.keys[0] = button.new('0',
         function () kp:input(0) end,
-        sx+kd, br, ks, ks)
+        sx + kd, br, ks, ks)
 
     kp.keys['A'] = button.new('A',
         function () kp:accept() end,
-        sx+kd*2, br, ks, ks)
+        sx + kd*2, br, ks, ks)
 
-    edge:set(m, "down", kp.room)
+    edge:set(kp, "down", kp.room)
 
     register(kp)
 
@@ -70,12 +70,21 @@ function m:input(n)
     end
 end
 
+function m:oncorrect()
+    log:log("Correct!")
+end
+
+function m:onwrong()
+    log:log("it seeems that the number does not match.")
+end
+
 function m:accept()
     if self.number == self.code then
-        log:log("correct!")
+        self.state = 'correct'
+        self:oncorrect()
     else
         self.state = 'wrong'
-        log:log("it seeems that the number does not match.")
+        self:onwrong()
     end
 end
 
@@ -94,13 +103,21 @@ end
 m.draw = window.draw(function (self)
     love.graphics.setLineWidth(3)
 
+    -- start drawing keypad
+
     -- draw indicator box
-    love.graphics.rectangle('line', self.padx, self.pady, self.indicator_width, self.key_size)
+    love.graphics.rectangle('line', self.pad_x, self.pad_y, self.pad_width, self.key_size)
+
+    local function display(str)
+        love.graphics.printf(str, self.pad_x + 5, self.pad_y + 5, self.pad_width - 8, 'right')
+    end
 
     if self.state == 'normal' then
-        love.graphics.printf(tostring(self.number), self.padx + 5, self.pady + 5, self.indicator_width - 8, 'right')
+        display(tostring(self.number))
+    elseif self.state == 'correct' then
+        display("correct")
     elseif self.state == 'wrong' then
-        love.graphics.printf("wrong", self.padx + 5, self.pady + 5, self.indicator_width - 8, 'right')
+        display("wrong")
     else
         error("keypad is not in a defined state")
     end
@@ -115,9 +132,11 @@ end)
 m.mousepressed = function (self, x, y, button)
     local x, y = x - self.x, y - self.y
 
-    for i, v in pairs(self.keys) do
-        if v:mousepressed(x, y, button) then
-            return
+    if self.state == 'normal' then
+        for i, v in pairs(self.keys) do
+            if v:mousepressed(x, y, button) then
+                return true
+            end
         end
     end