GPS is one such example. Some of us can't imagine going out of town without it. What you might not know is that while that GPS device tells you where to turn left, it is also storing where you go in its memory. Scotland Yard has started using this data to solve crimes:
Scotland Yard analysis of the [GPS] devices has helped solve dozens of investigations into kidnappings, grooming of children, murder and terrorism. Information about a suspect's whereabouts at particular times, their journeys and addresses of associates can all be discovered - if they have been using a GPS. The devices retain hundreds of records of locations and routes in their memory.
So all you criminals out there, make sure you use GPS whenever possible. We all know your actions are a desperate cry for attention.