In my entire life I have never, ever left money in a car. This is not a manufacturer problem. It's impossible to make a car totally secure. But an owner can enhance the security of his car in a number of ways. Faraday bags stop the signal from a key fob being transmitted so thieves can't boost the signal to steal the car. A more expensive solution is the Autowatch Ghost Immobiliser. The Ghost immobiliser uses the buttons in your vehicle, like those on your steering wheels and doors, to allow you to make a unique PIN sequence that must be entered before you can drive your car. There's also an iPhone app that connects to your vehicle and allows you to get in and drive without having to enter the PIN code. It's about £400 but it makes a car practically impossible to steal.