Cost: $450 installed
Time: N/A
Theory: A car alarm is designed to deter criminals who would steal a vehicle, and hopefully stop them. Hopefully they see the blinking LED and leave the car alone, if they do try to break in, the alarm sounds for 3 minutes and alerts the keyring remote (when within range).
Opinion: This alarm is definitely top quality, but I recommend telling the installer exactly how you want it set up, or they will take any shortcuts they can. You can have them activate passive arming, which will automatically arm the car if the engine is turned off and then you leave the vehicle. It basically starts a 30 second countdown and then automatically arms the vehicle. They will also most likely not tell you all the features, so be sure to research the exact alarm you want before you have them install it, and then direct them every step of the way and thoroughly read the instruction manual. Overall, I am very pleased with the alarm. When a car alarm goes off, I can rest assured that it is not mine, because the keychain will notify when it is.