There are a few ways to trick any potential thieves who look in your window to see what you have in your car if you don't have an alarm.
Most decks have a detachable face so that you can take it off and put it in its case to either hide away or take with you if it is worth it. This way the thief can't see your fancy deck and they'll only see a blank spot.
Another trick that can make it look like you have an alarm would be to get an LED light (usually red) that is several inches long and either flashes or moves the light back and forth like a real one would. Even a dark but still legal tint would be worth thieves not being able to peek in your vehicle.
If you have spent over $1000 on your car audio system, then I would definitely recommend getting a car alarm, especially if you live in a bad neighborhood. There are many different types that you can get that will make stealing for thieves next to impossible. Some give a warning and some will zap you. Even if the thief cuts off the battery power there are alarms designed to still sound the siren without battery power. From vibration detection to touch detection, there is an alarm for you.
I would not want to spend a large sum of money on a sound or video system and then have it stolen because that would be a huge waste of money. Depending on what extent you want to take your vehicle's security to, most alarms range in price from $40-$500. It would probably all depend on what kind of vehicle you drive or how much money you have put into your car.
