My understanding is that it requires an ISAT (or TECH-II, I guess it depends
on model year of car) device (dealer or independent saab specialist) to
program the system to accept a new remote.  Once the car and the remote are
synchronized though, if you have a battery failure in either the car or the
remote, you should be able to stand by the vehicle and push the door
lock/unlock button 5 times within a minute and have the remote
re-synchronize with the alarm system, but only after the two are synched by
the service tech's computer device.