My house has remote control keys (as well as regular keys). It's very convenient, I have no idea how secure it is. Anyway, I lost one of the keys and bought a new one and had some trouble following the Japanese instructions. I got it eventually, so here's the procedure.
First note, you can't just add a key, you have to wipe the system and add all of your keys back in one go.
The original Japanese docs are here and here. That'll make it clear how to get access to the register/clear button for you lock.
So, here's the procedure, I'm not exactly sure that all parts are necessary but this worked (you might want someone else around to do the press-and-hold part. Apparently you have 20s to do it all. I don't know how strict that is.
- Put one of the metal keys in your pocket - you wouldn't want to lock yourself out!
- Open the door.
- Twist both the top and bottom cyclinder closed and then open again. I suspect this isn't necessary but it's no harm.
- Remove the cover at the top of the top cylinder.
- Press the register/clear button for 5 seconds, until it makes a long beep sound. You have cleared all the keys off the lock, none of your remove control keys work now.
- Press and hold the register/clear button, keep holding it while you do the next steps.
- Take your first key and press lock then unlock then lock and unlock again. You should hear short beeps for these presses (I'm not 100% sure that I heard a beep for each one but definitely for the first lock press).
- Now take each of your next keys and press lock then unlock. Unlike the first key, you only need to do it once per key.
- Let go of your register/clear button.
- Put the cover back on the top of the top lock.
You can watch this video too. It's for a different model but gives a clear idea of the registration method.
