The Sensor Under the Public Bench

An urban design company offered the council free sensors to measure use of public benches. Planner Jo imagined evidence for installing more seats along steep streets. The devices recorded when someone sat down and how long they remained. Only later did she learn that they also collected nearby phone identifiers to estimate repeat visits.

The company insisted that the identifiers were transformed into anonymous codes. Jo asked whether the same code could still be followed from bench to bench. It could. Although nobody's name appeared, a person's daily route might become visible. The councillor responsible for the trial argued that the council needed better information than occasional observations made by volunteers with notebooks.

Jo took the company's engineer to a hillside bench used by older residents. For twenty minutes they watched people stop, talk and leave. The engineer explained that the phone data helped distinguish repeated visits from many different users. Jo explained that the planning question was simpler: whether the seats were occupied when people needed them. They agreed to test a version that counted pressure on the bench without detecting phones.

The resulting data was less detailed. It could not tell the council how many distinct people benefited, which disappointed the company. It did show that several uphill benches were occupied for much of the afternoon. The council approved two more seats. Jo sat on one during her lunch break, aware that her presence was being counted. She was equally aware that the bench would forget her as soon as she stood up.