Phone sensors can save lives by revealing what floor you are on

Knowing the location of an emergency caller can be a matter of life and death. But sometimes those seeking help are too panicked to speak clearly or don’t know where they are. Some callers don’t feel it is safe to speak at all, simply calling 999 or 911 in silence.

Now William Falcon and Henning Schulzrinne at Columbia University in New York have come up with a way to use a smartphone’s sensors to pinpoint not only where in a building a caller is located, but the floor as well. By combining GPS, signal strength and atmospheric pressure – using the barometer that many smartphones now contain – the pair created an app called Sensory that could identify how high up a caller was. Sensory is available online but the pair hope the system might be integrated into future smartphones.

The first step is to detect when someone is inside a building. “The GPS coupled with the strength signal of your phone gives a strong indication of whether you’re indoors or outdoors,” says Falcon. But what floor? Many smartphones, including all iPhones released since 2014, can now detect their elevation above sea level. This gives the altitude, but that doesn’t translate directly to floor number because the distance between floors can significantly vary from building to building.

To solve this problem, Falcon and Schulzrinne tracked volunteers who repeatedly visited different floors of certain buildings. Movement data was clustered at certain altitudes, revealing distinct floors.

Storey time

The pair also used plans of 1100 New York buildings to work out the average distances between floors in residential blocks versus office blocks. This meant that anyone in a building where data hadn’t previously been collected could also be located, provided the type of building was known.

Falcon tested the app by visiting 63 random floors at five New York buildings, including the Rockefeller Center. In 91 per cent of the tests, the system was accurate to within two floors.

Binghao Li at the University of New South Wales in Sydney thinks the new approach is interesting, but says the pair exaggerate how much of an improvement over existing systems it is. Li and his colleagues have developed a system that estimates floor location using Wi-Fi signals.

Having multiple options is a good thing, however. Locating emergency callers accurately in high-rise buildings is vital, says Kevin Kupietz, who teaches industrial safety and emergency management at Elizabeth City State University in North Carolina.

It could also keep responders safe themselves. “If a firefighter is able to more efficiently be directed to the exact location, including floor, the less time the responder is in the danger zone and the less chance of them becoming hurt,” he says.

The Metropolitan Police Service in London also welcomes the idea. “Any development that significantly assists emergency services in identifying the exact location of callers using mobile phones could be of assistance to us,” says a spokesperson.

Reference: arXiv, arXiv:1710.11122