The following makes are GM vehicles: Buick, Cadillac, Chevrolet, Geo, GMC, Hummer, Oldsmobile, Pontiac, and Saturn.
Many, but not all GM vehicles, are equipped with factory keyless entry. Having power door locks is a prerequisite but not proof that the vehicle was built with factory keyless entry. Many vehicles have power door locks without keyless entry.
The picture above is the GM Service Parts Identification Sticker. It is located somewhere inside the vehicle. On most GM vehicles it is in the glove box. If not there, it can be in a few other locations. In a 90s Cadillac sedan I found it in the spare tire cover. In a early 00's Cargo Van I found it on the door frame of the rear hatch. In a 1990s Firebird I found it inside the lid of a lockable compartment in the trunk. In an 06 Impala I found it on trunk floor beneath the carpet. However, most of the time it is in the glove box.
The following are codes which we know to be associated with factory keyless entry. If you have one of these then you have factory keyless entry: 5L1, A97, AE5, AE6, AP3, AP5, AP7, AU0, AU5, AU8, AX3, and K92. Also, if you have both these codes together: M82 and ATG, or ATG and BTV.
If you notice in the sticker picture above, the 5th code is AU0. That indicates that my wife's truck is equipped with factory keyless entry.
If you can not find your GM parts identification sticker, there is still an easy way to find out if your vehicle is equipped with factory RKE. Jot down the VIN number from the VIN plate where the windshield meets the dashboard on the driver's side (looking from outside) or from the production sticker on the driver side door frame (the production sticker is not the same as the parts ID sticker). You can also find your VIN number on the vehicle title, registration, or insurance documentation. Call your local GM dealer, ask for the parts department, and giving your VIN, ask if your vehicle is equipped with factory keyless entry. If it is then you can order a factory remote. If not, and you want to have remote keyless entry, go to an alarm shop or Best Buy to have an aftermarket system installed.