Will you be getting behind the wheel after a glass of wine or a beer this weekend? Do you think you're okay to drive? In the future, your car will decide for you. Nissan has developed a prototype car that monitors a driver's sobriety and, if it decides they've had enough, it will immobilise the vehicle.The anti-drink driving car uses several devices to monitor a driver's alcohol levels. There are odour sensors in the gearlever and the seat that measure the presence of alcohol in a driver's perspiration as they attempt to set off. If the system thinks levels are too high, it won't let you drive off, and an audible alert is sounded.If you manage to trick those sensors, there's also a facial monitoring system – a bit like that on the Lexus LS – which monitors the driver's state of consciousness through looking at the eyes. When the system detects signs of drowsiness, a voice and message alert is triggered, and the seatbelt tightens.Finally, there's a system that checks your driving and, if it's erratic, sets off an alarm and tightens the seatbelt.Nissan is already testing a system in Japan that uses an on-board breathalyser. The driver must use the system before they can start the car, but it won't work if they've had too much to drink. Volvo is also working on a similar system. Of course, the best way to make sure you're okay to drive is not to have a drink at all. We'll be taking the bus.