Advances in GPS technology in recent months have meant that SatNavs can now tell when a driver is starting to become drowsy at the wheel and will talk to the driver more.
"It grew out of lane assist," said Thomas Thompson, map co-ordinater for a rival SatNav manufacturer. "When the SatNavs can tell which lane you're in, they can tell when you're beginning to veer. This is one of the signs of sleepiness."
Additional sensors have been added to the units to detect temperature and the number of people in the car as an adjunct to the voice recognition already present.
"Using the available information, we can fairly accurately calculate how tired the driver is," said Thompson. "The unit then activates it's anti-drowsy software."
The unit changes the voice to a more strident female that issues more frequent instructions.
"Tests have shown that for moderate drowsiness," said Thompson, "that this is enough."
Should the problem persist, the SatNav increases its efforts.
"If simply increasing the frequency of instructions doesn't help," said Thompson, "the unit then calculates the nearest service station, if you're on a motorway, or rest-stop if you're not. It then provides instructions to the driver to visit and get a coffee or have a rest."
For drivers who follow these instructions, then the problem is usually solved.
"Some drivers insist on continuing on past the services," said Thompson. "These are what we call the excessively tired. In these situations, the unit waits until there is an unexpected sudden decrease in acceleration and then rings the police and an ambulance giving the precise GPS co-ordinates of where the driver has gone off the road and into a tree."