A remote starter for cars can be installed on vehicles that already have an alarm installed. A number of the higher end alarms come bundled with a remote starter. LCD alarms allow you to turn the interior lights on in the vehicle, and many systems let you start the vehicle with a push of a button. If your alarm does not have a remote starter bundled with it, you can install a standalone starter. Remote starters are widely available and fairly inexpensive. Unless you are comfortable working on a car, they should be installed by a professional.
For more info, see Most Reliable Car Alarm Systems