Consider two different security systems for your car. Both cost about the same.
One (LoJack, for instance) silently sets off an alarm for the police to come chase down the car thief. In the former, the thief doesn't know he's being tracked, but it may take some time for the police to find and catch him. Meanwhile, the thief could do some serious damage to the car as well as hand off any valuables therein before the police arrive. Most likely the thief will be caught, but possibly only after causing damage.
The other has a conspicuous decal stating that the car is protected, and will set off a very loud alarm in addition to notifying the police. Also assume that people don't ignore car alarms like they do in reality and will call the police. In the second case, knowing that the police will arrive shortly because of the alarm, the thief is mostly likely to move on to another car.
So which system do you buy?
Would you choose a visible security system or an invisible one?