Found this on the car101.com website. I'll try it tomorrow and see if it works.
CODE ALARM SYSTEM information is always subject to change and correction
Used on: Impreza 1996-2001 Legacy 1995-1999 Forester 1998-2000
Lock: Left button will lock all doors. Double chirp indicates locked. Unlock: Right button will unlock driver's door only. Hold unlock button app 6 seconds, it will unlock all doors including rear gate. Single chirp indicated unlock. If the car chirps or lights flash 4x the alarm was triggered. Panic. Press both buttons to activate emergency honk and flashing lights. Valet mode: With optional alarm only Press the red alarm button on the left of the steering wheel. The light will quickly double flash. To re-set back to normal mode, press the red alarm light button again
Battery failed and lights flashing? Parking lights will flash when the vehicle's battery is disconnected and reconnected. To stop lights from flashing, either: Press remote transmitter “UNLOCK” button once OR turn the ignition switch to the “ON” position and press programming button for one second (see below). The vehicle interior (courtesy) light and door open warning light (DOOR AJAR indicator) will then illuminate for 60 seconds when the ignition is turned off, or until the doors are locked with the remote transmitter. Yes, the dashboard instrument panel lights will flash when the parking lights flash.
Programming or Overriding the Alarm when you have lost the remote Open driver's door. Turn ignition key to 'On' Press and *hold programming button* in (see diagram, button under dashboard) After 15 seconds the the door locks will cycle 3 times. Do not release Programming button Press lock (left) button the remotes to be programmed. The door locks will cycle one time. Exit programming mode by releasing Programming button under dashboard and turning key to off.
Code Alarm Programming Button is under dashboard on the kick panel by the driver's left knee, left of the steering column. If you can't find it, it might still be tucked up in the wiring harness higher up in that same general area. The botton is recessed in a plastic ring (see diagram). This button must be pressed while programming remotes or if the battery was disconnected and the lights are flashing.