Yeah i was doin some research on alarms like a month ago, tryin to get one for my new car.. but i still havent gotten one yet.
If you want a straight "Car Alarm" i would say got with a Viper or Clifford.. u can get the alarms with the LCD screens that show if someone is messin with ur door/hood/trunk whatever.. but the thing is it has short range and if ur not in range u wont get a response. there around i think $300-$400..
The other i was lookin at was Lojack.. which seems pretty good.. they put a device in ur car.. they dont show u were its at, can be in like 28 different places.. yada yada, If u notice ur car is gone, u call to activate it, and police can use there radio to track it down.. within a couple hours.. but that could be too late. Because its up to u to notice when ur car is not there. But then Lojack has an Early warning opition, for like $100 more.. when the hidden lojack device detects that the car is moved.. it will send out a message to ur phone, email, cell phone, ect. to let u know.. so u can call it in quicker. So for the Lojack unit its like around $500-$600, $100 for Early Warning, and they say every 2 years u should have it checked on to see its still working properly which is like $25.
So ur only really safe if u have both.. but thats a lotta money.. i think the best thing if u can afford it would be get a Lojack, Early warning and a cheap "car alarm" just it alerts people around ur car if someones messin with it.