They are supposed to make getting around easier.
But over-reliance on sat-navs could leave us completely lost, a study has suggested.
Scientists think our memory for places is like a mental map which we have learnt from looking at a real map of where we live.
Researchers tested 26 residents of a town, all of whom had lived there for at least two years.
They were put into a virtual-reality headset which showed a 3D model of the town at locations familiar to them, but under fog.
They had to point to a place they could not see, for example the fire station. They were then asked to draw a map of the town, including all the test locations.
Though participants' maps of Tubingen, Germany, differed, the results showed everyone performed most accurately when facing north.
Previous theories of how we find out where we are maintained that the further away an invisible location is, the longer it takes us to point in its direction.
But given the accuracy of locating northwards, researchers concluded all participants had seen and remembered a map of the town at some point.
Researcher Tobias Meilinge thinks GPS devices will eventually erase these memories. He said: 'If somebody doesn't care to learn the environment, that's fine.
'But they shouldn't complain if their mobile is not working and they are completely lost.'
- DAILY MAIL