Over the last few days the small white boxes have been spotted at the Windang and Shellharbour road intersection, along Five Islands Road and Masters Road, among other locations.

They have prompted rumours on social media that they are part of the government's move to install cameras to catch people using their mobile phones.

"Warning: The NSW government has started rolling out the new mobile phone detection cameras," one post on Facebook stated.

"The intersections at Warilla McDonald's and at Windang Hotel have the new cameras installed."

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While Transport for NSW has said the Illawarra will be a location for the mobile phone cameras, none have yet been rolled out anywhere in the state.

The rollout of cameras is due to start in December and the cameras will operate in warning mode for the first three months before people cop a $344 fine and five demerit points.

"There is strong community support for more enforcement to stop illegal mobile phone use," Transport and Roads Minister Andrew Constance said.

The planned locations are believed to be secret and the Mercury understands that, unlike speed cameras, there will be no signage warning motorists of the mobile phone camera detector's presence.

As for those odd devices that have people concerned, well, they're been set up by Transport for NSW to monitor traffic flow across the city.

A Transport for NSW spokeswoman described them as "a part of standard network monitoring".

"This investigation work is essential to understand the current use and performance of roads on the NSW network," the spokeswoman said.

The devices were set up over recent days and will remain in place for two weeks.

The spokeswoman said the devices are at several locations, including sections of King Street and Five Islands Road between Warrawong and Cringila and along Springhill Road and Masters Road in Wollongong.

They are also along Shellharbour Road between Windang and Shell Cove, Lake Entrance/New Lake Entrance Road between Warilla and Oak Flats, and on the Princes Highway and M1 Princes Motorway between Figtree and Oak Flats.