They have a push button 2x or 4x selector. Is that what you mean?
Polaris 4x4 system works as follows. It has a 2 wd and 4wd selector. When in 4wd mode the front tires will not kick in until the back tires turn 20% faster than the fronts. When this occurs it kicks into true all four wheel drive. When 4x4 is not needed anymore the front end kicks out until needed again. Works like auto 4x4 mode on 1/2 ton GM trucks.