The best way to figure out how to program an alarm is to read the owners manual. There are a number of different Autopage alarm systems and not all of them use the same sequence for programming. If you have misplaced the owners manual, Autopage.com has a very helpful download section that lets you download most of their manuals. A typical sequence is as follows: Put the key in ignition and switch from Off to On three times. Next, push the valet switch on the Autopage alarm twice, holding the button until there is a chirp. This signifies the program sequence is ready. Press any button on your remote, and when you hear another chirp the programming has been successful.
For more info, see How to Install an Autopage Car Alarm