HELSINKI, Finland — Helsinki’s airport will be the world’s first to track passengers to within feet, a plan being hailed as a technological breakthrough — and drawing scrutiny from privacy advocates.

Sensors will monitor all mobile phones with Wi-Fi access turned on from parking lot to takeoff, helping to observe crowding and prevent bottlenecks at the two-terminal airport which 15 million fliers pass through a year.

Passengers opting in through an application will also receive offers from shops and restaurants, as well as gate and flight information.

While the technology has clear benefits, companies must tread carefully to adopt it as such systems can be perceived as enabling the monitoring of unwary people.

Walkbase, based in Espoo, Finland, is providing the indoor-positioning system for the airport.

The Helsinki airport operator, Finavia, won’t see any personal information about the user or the device as all data stays in an aggregated form, said Tuomas Wuoti, chief executive officer of closely held Walkbase.