Juiced Hybrid, the company that makes the gadget, says it can improve gas mileage by up to 30%, which could translate to a savings of $560 a year for the average commuter.
In addition, the company says Kiwi can help reduce a car's carbon emissions by 1.8 tons per year.
The Kiwi can be used in any car made after 1996, including non hybrids.
The device scores how efficiently a user drives based on measurements of smoothness, drag, acceleration and deceleration. Drivers are challenged to achieve a better score by altering their driving habits.
The Kiwi, which was designed by a former race car driver turned hybrid-enthusiast, costs $399.