A "Full Feature Remote Start" is a remote start that can also control your car's door locks for keyless entry.  If your vehicle has an electronically operated trunk or hatch release, the remote start will operate that too.  Full feature remote starts will come with two remote controls, each having 3-5 buttons. Pictured Sample:  The Excalibur RS310 Close Window

A "1-Button Remote Start" is a remote start that will only stop/start your car.  It will not control the door locks or trunk release.  1-Button remote starts will come with two remote controls, each having 1 button that is used to start and stop the engine. Pictured Sample:  The Crimestopper RS4 Close Window

An "Add-on Remote Start" is a remote start is controlled by your existing factory or aftermarket keyless entry fobs.  Pressing Lock>Unlock>Lock on your fob will activate the remote start. Add-on remote starts do not come with an antenna or remote control. Pictured Sample:  The Excalibur RS110 Close Window