How do you program 2008 Cadillac STS fob?

To program a 2008 Cadillac STS key fob, first, enter the vehicle and close all doors. Insert the key into the ignition and turn it to the "On" position without starting the engine, then back to "Off." Repeat this process twice, then turn the key back to "On." Press and hold the "Lock" and "Unlock" buttons on the fob simultaneously for about 15 seconds until the locks cycle, indicating successful programming. Repeat for additional fobs, then turn the key to "Off" to complete the process.