This battery Switch can serve two purposes..

First of all, a problem a lot of people have personally experienced is the spring battery blues.. you get into your car after too many weeks of it sitting in the garage, turn the key and nothing happens. The alarm system seems to have drowned the battery.
This does not only mean the battery needs charging, in nine out of ten cases, it also means buying a new battery. So far for the good feeling of getting your car out of the garage again :(

The other purpose is a very effective anti theft system.. When using a 2A bypass fuse, you can undo the main battery switch (turn clockwise) and all low power systems, such as the alarm system will remain powered.
Once someone gets into the car and tries to start her, the fuse will blow. There's no way you can get away without power!

It is important to understand that you will need to remove the fuse if you are storing the car for a longer period, otherwise, the battery will be drowned at the end.

This kit contains the Battery Switch with a key and a cap. This can be used as the ultimate starter interrupter.

Basically, this is the same kit as the Battery Interrupter, but a switch for easy access. (Also suitable for racecars)