Google mobile search stores the most recent search term in a text file, and mobile browsers cache content along with the accompanying URLs and graphics. Nokia handsets have started automatically geo-tagging photographs, so locations and times can also be established with ease, while the iPhone stores a screenshot of every application as it’s closed (so it can zoom into it when the user returns). Even basic handsets can provide data from unlikely sources: the predictive-text dictionary is a fine source of names and places, even if the presence of an unusual name doesn’t prove anything it can be hard to explain. These days even the cheapest phone is likely to have a camera, with photographs that can be vital evidence; and even something as apparently innocuous as the last Bluetooth search (which is generally cached) can turn up interesting snippets of information in the right circumstances.

Will your mobile squeal to the police? | The Register