Previously I had a isolating switch on the battery, but I realized that in the event of a fire, you would have to pull over the car, get any passengers out, pull up the carpet, pull out the battery access panel in the floor and disconnect the battery via the switch on top of the battery.
Now that could take a bit of time, especially if there was panic involved.
At a DVHCC meeting in February 2010 there was a presentation by Michael Hartman on fitting a Battery Kill Switch inside the cabin. That's for me I said, and had the job done within 24 hours.
Now, if I need to isolate the battery, I reach down below my knees, and turn off the switch which is located on the lower seat frame, well within my reach, even with a passenger.
Very quick, very simple, and my insurance company loves it, as with key removed from the switch, I have another anti theft device.
When I park or garage the car its now a simple process, turn off the engine, remove the key, turn off the battery switch, remove the key.
The switch I used is the type as below, and is connected on the negative side of the battery.