Siphon Gasoline -- Possible?

If you are worried about someone stealing you gas I think i saw at walmart this spiral metal thing that you screw down your gas filler neck, it goes in deep enough to allow the gas nozzle to fit in and add gas, but won't allow a hose to go more than 4 or 5 inches down the filler neck as the gizmo spirals towards a point.

On average I probably only have 5 gallons in at any given time, and the Prius has locking gas door like all toyotas so why bother? now my isuzu rodeo I bought a locking gas cap to use 3 seasons of the year and left it unlocked in the winter so it wouldn't get stuck, I figured nobody would risk jail time for a little gas in freezing cold temperatures.

 

The Prius comes equipped with an anti-siphon screen - no need to add another one.

Tom