Having these handy little devices on your steering wheel, hand brake and gears, is a big deterrent for car thieves. These devices prevent you from using the steering wheel to steer, from lowering the hand brake to drive away, and to change the gears.
It cannot be guaranteed that every thief will be deterred, but most of them will see the security measures you have taken and be discouraged. If your car is parked in an isolated parking, they might still try, because there aren’t a lot of people to catch them, and they have more time to try and steal your car, and valuables.