PARIS – Automobiles Citroen filled out another position in its letter-number lineup, presenting the C4 at the Mondial de l’Automobile in Paris.

The car, which will compete with models such as the Renault Megane, Peugeot 307 and Volkswagen Golf, offers a technology that’s a first for any segment – a lane-departure warning system.

The device puts a virtual rumble strip under the driver’s flank when he changes lanes to the right or left at a speed over 50 mph (80 km/h) without signaling first.

By teaching drivers to signal lane changes, the system makes the roads safer for other drivers, says Citroen Managing Director Claude Satinet. And it protects a drowsy driver by waking him up when he drifts out of his lane, he adds.

The system uses infrared sensors to watch the lane markings. Valeo SA, which will introduce a system based on cameras in the Infiniti FX in North America next year, worked on the algorithms and control unit with Citroen.

Faurecia SA, the seating supplier controlled by PSA Peugeot Citroen, developed the actuator in the seat that vibrates on the side to which the car is drifting.

A second unique technology among current cars is the steering wheel that moves around a fixed center containing switches for radio, cruise control and other functions.

Switches are always visible, no matter how the steering wheel is adjusted, and they remain in one place, even when the wheel is turned. Having the fixed position allowed supplier Autoliv Inc. to redesign the airbag as a cylinder instead of a circle, so it is better adapted to the shape of the human it is meant to protect.

The C4 also introduces an information screen in the center of the dashboard that adjusts itself automatically to the ambient light, so that speed and other information always are visible.

A final C4 innovation is a perfume dispenser built into the dashboard.

“You’ve all seen horrible things hanging from the rear-view mirror to add scent to the cabin,” says Satinet. “We decided to do something about that.”

A small wick containing two months’ worth of scent to be distributed by the ventilation system is inserted in the device and activated or stopped with the push of a finger.

Meanwhile, Citroen shows off the revamped C5, which competes with cars such as the Volkswagen Passat in the upper-medium segment. The car’s major facelift tat includes adoption of the C4’s lane-departure warning system and other C4 technologies, such as bi-Xenon headlights that turn with curves and a cruise control/speed limiter.

Two other cars demonstrate Citroen’s move to appeal to environmentally concerned buyers. The Citroen C3 Stop & Start, with its alternator-starter motor, was presented here. Citroen expects to sell 2,000 units by the end of the year, at a price slightly below that of a comparably equipped normal C3. (See related story: Citroen Stop-Start C3 Priced to Move)

That appeal to drivers who care about a 10% fuel savings is echoed in the presentation of Citroen’s first natural gas vehicle aimed at private buyers.

Next year, Citroen will begin selling a bi-fuel C3 with a 70-hp 1.4L engine. With tanks full of natural gas under 2,900 psi (200 bar) of pressure, the car has a range of about 124 miles (200 km) on natural gas and 311 miles (500 km) on gasoline. Running on natural gas, the car emits 20% less carbon dioxide than with gasoline, a savings similar to that of diesel.

At the same time, the French natural gas company Gaz de France announces it will make compressors for use in private garages so people can fill up their tanks at home, while they sleep.

“If you’ve driven 50 km (31 miles) during the day, using about a fourth of the fuel, it will take about four hours to refill the tank” with the home unit, says Michel Valet, the executive responsible for new energies at Citroen. The unit does not need to be watched, and it will switch off automatically when the tank is topped off.

While prices are not settled, Citroen intends to price the car between a diesel and a gasoline car. Renting the home compressor and buying the natural gas is intended to cost less than diesel fuel.