One of the things that's great about modern Wi-Fi is how far-reaching signals from your router can be, especially if you've optimised the placement of your gear. But, of course, this wide coverage comes with a downside too: your Wi-Fi network probably extends to your neighbours' homes and out onto the street, and if you don't take steps to properly secure access to your data, any snoopers can ride on your bandwidth.

But what if Wi-Fi was somehow smart enough to bar access to people who weren't you? That's the thinking behind a new wireless system developed by researchers at the Massachusetts Institute of Technology (MIT), which is able to physically locate all users on a particular network with extreme precision, down to within tens of centimetres.

Not only would this kind of technology mean we could dispense with Wi-Fi passwords, but it could also enable better security for our devices by only letting specific, legitimate users access data.

The system, called Chronos, locates users by calculating the amount of time it takes for data to travel from their device – say, a notebook or smartphone – to the router's access point. Depending on your physical distance from the router, it will take a longer or shorter amount of time for data packets to reach the router, and Chronos is basically able to figure out your location depending on how long that is.

The researchers tested their prototype in a two-bedroom apartment with four occupants, and the system could correctly identify which room each resident was in 94 percent of the time. In another experiment, set in a cafe, Chronos had 97 percent accuracy in determining legitimate users inside the building, and 'intruders' lurking outside. (Amusingly enough, a survey from a few years back found that almost one in three Americans admitted to stealing Wi-Fi in this way.)

According to the researchers, Chronos, which can run on only one access point, is 20 times more accurate than existing systems that can localise the position of a user (by means of triangulating the person's position from multiple routers).

Chronos instead works by hopping between different frequency channels, gathering numerous different measurements of the distance between the access point and the user. It then stitches these all together to figure out the actual distance, which is how it can be accurate to within centimetres.

"By devising a method to rapidly hop across these channels that span almost one gigahertz of bandwidth, Chronos can measure time-of-flight with sub-nanosecond accuracy, emulating with commercial Wi-Fi what has previously needed an expensive ultra-wideband radio," said Microsoft researcher Venkat Padmanabhan, who was not involved with the study. "This is an impressive breakthrough and promises to be a key enabler for applications such as high-accuracy indoor localisation."

And that high-accuracy localisation won't just be useful for blocking people from stealing your Internet. The same detection abilities could also help you find lost devices or control things inside your home, whether mundane home appliances (like air con) or more forward-looking applications.

"From developing drones that are safer for people to be around, to tracking where family members are in your house, Chronos could open up new avenues for using Wi-Fi in robotics, home automation, and more," said one of the researchers, Deepak Vasisht.

"Imagine having a system like this at home that can continuously adapt the heating and cooling depending on number of people in the home and where they are," added co-author Dina Katabi. "Eliminating the need for cooperation between Wi-Fi routers opens up many exciting new applications for localisation."

The researchers' paper was presented at this month's USENIX Symposium on Networked Systems Design and Implementation (NSDI '16).