The Brussels public transport service and its agency Mortierbrigade decided to ring a few changes recently. The first step was to install innocuous-looking posters promoting the city’s tram service. But a clever bit of electronic wizardry meant that every time someone pressed their remote car key nearby, the poster made the tram’s distinctive “ding-ding” noise, and the headlights on the tram image lit up. In fact, the poster’s software was wired to respond to the frequency of car keys. The message was clear: to get the city moving again, take the tram instead of your car. Drivers could even use their keys to claim a free tram ticket from a slot on the poster. So the ring also added a bit of zing to their day.