I just thought I would make this thread to show what you should get and what's out their. Most people have Viper/DEI alarms so I'll show what you can get. Any other people are welcome to chime in, I believe if we can get enough on here it should be stickied so people who get aftermarket or modded factory alarms will know HOW to protect their gear. Nothing worse then coming back to your car and realizing everything was taken. It *****, trust me.
The first add-on I believe any alarm should have is a Backup Battery. They will keep your alarm going if your main battery is disconnected, so that it will draw more attention. The worst thing you need is an alarm that can be disabled with one cut of a wire. You can find them for about 40 Shipped on ebay, and they will go for about 16 hours if the battery is disconnected. It can power all the sirens, and will basically act as another battery for your alarm.
The next thing you want is Additional Sirens. They can make your alarm louder, and attract more attention. I've heard stories of people going absolutely gung-ho and their amount of alarms, some people going up to 20. I myself have 2, and am going to be adding another 2 soon. Smart places to put them would be near the brain of the alarm and near the back up battery, should a thief find them, you want it to be painful for them to turn them off. Also, Put them near your subwoofers or amps, so that it is also painful for them to take them out. Use security screws to slow the removal process so they have to listen longer. Any piezo siren will work, they all just have a negative and positive wire. I have seen them as low as 7 Shipped on ebay for the authentic DEI 513T siren, but you can probably find cheaper non-DEI sirens too. They all work pretty much just as effective. Also, remember to use a relay if you have more then 3-4 sirens and you want to add more.
Glass Breaking Sensor
A glass breaking sensor will detect the sound that glass makes as it is shattered and trigger the alarm Some professionals and expert thieves can break glass without causing too much of a shock, making it easy for them to get inside and and kill the brain without the alarm going off. A glass break sensor runs about 20 shipped on ebay, and can be a worthwhile investment if your brain is placed in a easier to reach spot.
The tilt sensor detects if your car is being tilted up by a jack and sets of your alarm. Some theives try to steal your precious and valuable wheels and tires, so this is a smart choice. If you have wheels and tires that cost a lot, you should most definitely get this add-on, as well as 1 or 2 locking lug nut sets. They run at about 35 shipped, which is so far the most expensive add-on, however, protecting your wheels (which can run quite a bit more then 35 dollars ) is essential. If your wheels are gone, you'll need a tow and a ride, so protecting them is a MUST.