Ok, very similar thing happened after i changed my battery.

You need to punch in the mastercode and then if you know what you're doing, go from there. I had action alarms come out and have a look at it for me and i need the actual keypad battery changed. I also called up Peel Subaru (Mandurah) and they were willing to help over the phone, but at the time i called up, it was Friday and i needed car for the weekend and the latest they could get the info from east was Monday. I got my batteries changed at Battery World O.P.

In conclusion, call Mandurah as they should have all the info to do it, if not, Action Alarms can come out to you.