The electric smart fortwo BRABUS will be premiered at Geneva’s 2009 edition and it will feature a state of the art lithium-ion battery. The German tuner wants to prove that a car that is friendly to the environment ca still be lots of fun driving. To help achieve that BRABUS uses various innovations out of witch we found interesting the one referring to the sound generator , this as part of their active safety strategy, that makes the car sound like a regular gasoline engined car through the power output. 
Smart press release: 

smart fortwo BRABUS electric drive: Exclusive, innovative and environmentally friendly 
     –  Exclusive show car with electric drive
     –  Top model with superior style
Environmental friendliness does not mean making sacrifices. The smart fortwo with its high quality equipment proves that a car that makes environmental sense can also have charm and be fun to drive – otherwise the innovative two-seater would never have attained its popular status. smart-BRABUS takes the smart fortwo to an even higher level.
In Genevaa near-series smart-BRABUS show car featuring electric drive and
a state-of-the-art lithium-ion battery will celebrate its world premiere. Here, ecology and a feast for the senses go hand in hand. The light and airy design of the smart fortwo BRABUS electric drive coupled with fine natural materials demonstrate harmony with the environment and at the same time elevate the pleasure of owning and driving such a high quality custom-tailored vehicle to an even higher level.
Exclusive matt green paintwork gives the vehicle a very elegant and trendy appearance. A white cabriolet soft top and LED daytime driving lights round
off the harmonious appearance of the exterior. The matching interior features leather and fabrics in the colours green and white.
The sports suspension with BRABUS "Monoblock VII" alloy wheels in a five double-spoke design and matt white exterior and interior applications convey a sporty and functional impression. For reasons of active safety the smart fortwo BRABUS electric drive is additionally equipped with a BRABUS sound generator which generates a sound specially developed for the smart electric drive via the power output.
The show car provides a look ahead at the series production. And as with all smarts to date, a smart-BRABUS variant will have a firm place here.

Source: Smart