Alarm wise, they make sirens with a battery system of there own and if the main power line to the siren is cut they still go off. Note if they spray shaving cream gel in the siren it won't make a sound, at least not one you will here. This in mind mount it somewhere they can't easily get to. There are also battery backups for the alarm itself to keep the system up completely if they kill the battery. Most alarms only have a shock sensor so if they are after your rims and take their time, they can jack the car up without triping a shock sensor. A motion sensor though will pick up a change in angle such as jacking the car up so that can help as well as a proximity sensor for detecting when someone is near the car.
All of these things if not installed properly can cause serious false alarms. Check your area and find a reputable installer. If anyone here on the list lives near you and know of one maybe they could post a few good installers and help you out.
Just realize that a good system is not going to $100, you get what you pay for and if you don't want to pay to replace stolen item invest in keeping them.
Also if you have a large amount of aftermarket items you may want to check and see if you insurence covers them in case of theft or if you are only covered with stock replacement.