An art project is hoping to highlight the issue of surveillance in modern society by using Bluetooth technology to track people without their knowledge or consent.
Loca sends texts to people describing their recent movements
Loca: Set To Discoverable uses a cluster of interconnected Bluetooth nodes in urban environments to track and communicate with people via their mobile phone, as long as their phone is Bluetooth-enabled and set to discoverable.
"Mobile companies have information about everywhere we go that gets generated every time we use our phone," Drew Hemment, an artist involved in the project, told BBC World Service's Digital Planet programme.
"We're looking at how we can have access to such information, by setting up an independent network that we create within a city centre that enables us to track people without their permission or knowledge - and send them messages as well."
The Loca team fix the nodes to traffic lights and pedestrian crossings at busy intersections, dressed in the bright orange overalls of municipal workers.
Other nodes are deployed in hotel lobbies, cafes and cinemas, placed in flowerpots, and buried beneath bar terraces.
The project was first presented at the ZeroOne Festival in San Jose in California, where it tracked 2,500 people and detected them over half a million times.
The attendees were also sent messages through bluejacking - the process of scanning for and connecting to other Bluetooth-enabled mobile devices without the owners' consent.
"That is actually a surveillance act - so every time you use Bluetooth you're actually looking to see what other devices are around you, and without disclosing who you are," said Mr Hemment.
"Someone received messages from someone who had intimate knowledge of their movements, that were written in such a way as to make them think that maybe they signed up to some social network, but forgot.
"Then, over the week, the messages got slowly more sinister - and changed from 'coffee later?' to 'are you ignoring me?'"
The messages ultimately directed people towards the Loca stand at Zero One, where people could scan their device and receive a personalised printout of their movements.
Some individual logs were over 100m long.
"A lot of people were very surprised that we were technically able to do it," Mr Hemment added.
The nodes are placed on walls and street furniture
"A lot of people wanted to talk about the issues that the project was raising, to do with how much of this data on our everyday movements is generated without our knowledge, and the issues to do with who has access to this information."
He added that ultimately, Loca is intended to equip people to deal with pervasive surveillance.
"I think art is a place where we can experiment and push the boundaries of technologies and the ways in which we use them," he said.
"Many technologies have social consequences. We really wanted to explore the ethics of these new environments, and to show people what's possible technically and ethically.
"If we can do this, could a supermarket do this?"