Generally aftermarket gives you a better range.. Usually half a mile to a mile vs the factory which usually isn't that great. Yes it will sound just like any of alarm if the alarm is armed but you have a wider range of extra sensors you can add on. Errors usually occurs from improper install. One thing about the factory system is if your CEL is on guess what.. Remote start won't work. Which can be a annoyance especially if it's something minor triggering the CEL. With aftermarket units you don't have this problem.
