If you want to find out which of your devices have successully connected to your local network or if someone is using your bandwidth without letting you know about it, you can scan your network the geeky way by entering command-lines in PowerShell, or the easy way by using specialized tools.
http://www.softpedia.com/blog/how-to-get-a-list-of-pcs-and-other-devices-on-your-local-wired-wireless-network-504256.shtml
http://www.softpedia.com/blog/how-to-get-a-list-of-pcs-and-other-devices-on-your-local-wired-wireless-network-504256.shtml