Car Alarm For 06 Jeep..HELP

Hey guys, I just bought a 2006 Jeep Liberty. It does not have a alarm on it, it has the key less entry with a panic button on it, but no actual alarm. The guy at the dealership told me that if somewhere were to get in to it without a key and try to steal it it would shut off in 10 to 20 seconds because it has no key code that connects. Does that sound right? My other question is, what if they hot wire it..will it do the same thing?

I really want to put a alarm system on it, but everyone is telling me not to, because it all ready has security & I can screw up my electoral in it. I do not know what to do.

Suggestions? Experiences?

Thanks!