As if you weren’t sick of (or completely immune to) targeted advertising on the internet, the next place it could crop up is on the walls. A UK university is testing a prototype ad screen in a corridor – the screen identifies passers-by via the Bluetooth signals from their mobile devices, and then software agents hold a bidding war in microseconds to decide who gets to display their content. The system will be able to differentiate between different people to ensure no-one sees the same ad twice. I think we just found another good reason to keep the Bluetooth on your phone switched off when you’re not using it.