Two words: "snake oil".

Don't waste your money. NONE of the devices that are supposed to
increase fuel mileage actually do so. NONE! If it were that easy to
increase fuel mileage, every car would come equipped with such devices
from the factory.

Either your car is in serious need of maintenance or you need to examine
and modify your driving habits. You should be getting mid-30's on the
highway @65 mph and probably mid-20's in the city.

When was the last time you replaced the air filter, spark plugs and wires?

Magnets will have no effect on fuel. The fuel is plenty broken up as it's
atomized into the cylinders. Provided there's no mechanical problems with
your car, about the only things that you can do to improve the gas mileage
is to make sure the air cleaner is clean, and use as thin an oil as is
recommended for the vehicle, given the outdoor temperature. Even those
things will only make a small difference, as long as the air filter doesn't
look like it's caked with mud.

dont waste your money, instead treat your vehicle to a new air filter..

One the magnet thing, it sounds like bull.  Sorry.

But I think something's not quite right on your milage.  I also have a
2001 Elantra stickshift, and the lowest I have ever gotten in city
driving is 24 mpg (with AC on), and I've gotten as high as 34 on the
highway on long trips.  Specifically, thanks to a logging program for
the palm pilot, I know I've averaged 28.23 mpg since 12/7/05 over the
last 9 fillups.  This is probably 2/3 highway driving.

Your car is 5 years old now, like other people have asked, have you
done the routing maintenance?  Spark plugs, wires, air filter, etc?  
(On a less relevant note, if you're over 60k miles have you changed
your timing belt?)

Just curious.
Ben

OOooohhhh - stay away from these.

Not too long ago, one of the auto sites (it may have been Edmunds) had one
of their advisors go out and buy a bunch of these techmo-gadgets (including
this one), and try them on a number of cars.

Wish I could find the report and just include the link, so you could see it
for yourself.

Suffice to say, none of these devices worked.  Worse, some of them ended up
causing REAL problems like fires and shorted wiring.  Even those that didn't
harm anything failed the tester's "common sense" test.

Bottom line - follow the advice of the others who have written you on this.
Stay away from these things.

Tom Wenndt