Apart from the radio, the sound environment inside a car consists of the mechanical noises of the running car and the electronic sounds added to help the driver. We focus here on the turn signal. We conducted a listening test with sounds of actual cars and found out that customers do not all share the same opinion. If all customers agree on basic sound characteristics (rhythm) related to the function of turn signal, some appreciate actual sound quality (timbre) whereas the others expect more creative sounds. Then, our guideline was to design sounds that work well with different car environments (materials,…). Modalys, a sound synthesis tool developed at IRCAM, suited our needs. Therefore, IRCAM/Sound Design team to formulate the problem in terms of methodology and to create sounds for us. The next step was to install the sounds in cars. In Renault cars, the turn signal sound comes from the dashboard. It is very simple (two frequencies) and easy to produce with the technology used (microcontroller and buzzer). We chose target sounds from the IRCAM database. To convert our wave files to car technology, the electronics engineer and the supplier had to better understand the performances of typical car components. In doing this, they discovered new capabilities. As such, the target sound guided further refinement. The implemented signals have a better sound quality without a major cost effect. The turn signal is not the only man-machine interface inside a car; other sounds are played. We have to insure the coherence of all such sounds. Future work deals with this task.