diff --git a/app/controllers/macs_controller.rb b/app/controllers/macs_controller.rb
index d26bc89..19fdea6 100644
--- a/app/controllers/macs_controller.rb
+++ b/app/controllers/macs_controller.rb
@@ -12,6 +12,8 @@ end
 load_and_authorize_resource :mac, :except => :create
 load_and_authorize_resource :user, :through => :mac, :except => [:index, :show, :scan, :import]
 
+before_filter :arp_lookup, :only => :new
+
 #require "active_record"
 require "optparse"
 #require "rubygems"
@@ -136,7 +138,10 @@ end
     end
   end
 
-
+def arp_lookup
+  @ip = request.env['REMOTE_ADDR']
+  @arp = %x(/usr/sbin/arp -a | grep #{@ip})
+end
 
 def scan
 Rails.logger.info "starting scan..."
diff --git a/app/models/user.rb b/app/models/user.rb
index 069582d..2604e15 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -15,6 +15,7 @@ class User < ActiveRecord::Base
   has_many :user_certifications
   has_many :certifications, :through => :user_certifications
   has_many :payments
+  has_many :macs
 
   validates_format_of [:twitter_url, :facebook_url, :github_url, :website_url], :with => URI::regexp(%w(http https)), :allow_blank => true
 
diff --git a/app/views/macs/_form.html.erb b/app/views/macs/_form.html.erb
index 61586dd..8287339 100644
--- a/app/views/macs/_form.html.erb
+++ b/app/views/macs/_form.html.erb
@@ -17,7 +17,8 @@
   </div>
   <div class="field">
     <%= f.label :mac %><br />
-    <%= f.text_field :mac %>
+    <%= f.text_field :mac, :value => (@mac.mac || @arp || nil) %>
+    <% if @arp.present? %><br/><em>Autodetected from your IP of <%= @ip %></em><% end %>
   </div>
   <div class="field">
     <%= f.label :note %><br />
diff --git a/app/views/users/show.html.erb b/app/views/users/show.html.erb
index bd47b8e..4b03487 100644
--- a/app/views/users/show.html.erb
+++ b/app/views/users/show.html.erb
@@ -93,6 +93,14 @@
   <% end %>
 </p>
 
+<b>Computers: </b><%= link_to "+ Add", new_mac_path, :class => 'btn' if can? :create, Mac %>
+<ul>
+  <% @user.macs.each do |mac| %>
+    <li><%= link_to mac.mac, mac %></li>
+  <% end %>
+  <% if @user.macs.blank? %><li>n/a</li><% end %>
+</ul>
+
 <p>
   <% if current_user.admin? then %>
     <b>Payments:</b>