Restrict by MAC address
Configure the access point with a list of MAC addresses that are allowed to connect to the wireless network. Once you have configured MAC filtering on the access point, any system that does not have a listed MAC address is denied access to the network when it attempts to connect.
MAC filtering by itself is not a very secure feature. An adversary could use a program such as Kismet to view a list of clients and their MAC addresses that are connected to your network. With a list of valid MAC adresses, the adversary could then spoof an address.