Is it possible to buy a factory alarm for a 3rd gen. MAby get one for a 4th gen and add it. I would even consider an alarm from a 200 Pathfinder or such. My roomamte had one and its got awesome range. I want a factory keyless because they offer a very long range and that is what i want.

 

you already have one.
All 3rd generation Maximas have alarms.

 

i know it has a factory alarm, but i am more interested in having a actual remote for keyless entry.

 

look on ebay; they have tons of them for under $50