I assume you're trying to keep others out of your wireless modem, and the password isn't good enough?
Your router is most likely set up to hand local IP addresses dynamically via DHCP. That means no device that connects is guaranteed to get the same local address, so filtering on the IP address isn't going to be very useful.
A more common solution is to filter devices by MAC address, listing only those that are permitted (or alternately, rejecting specific addresses, but that's a less useful setting). Your router should have a page for doing that somewhere in the wireless area.
ipconfig /all will show the physical address (same as mac address) for a PC
For android, go to Settings->About Device->Status to see the mac address
As for accidentally locking yourself out...the above only applies to the wireless setting. You can always plug a PC into the router with a physical network cable to get back in. Highly recommended anyway when messing with router settings. In fact, disabling wireless administration entirely is a very good security step, in my opinion. Then people need physical access to even start to mess with it.