Also known as Call a Bike, free floating bike or fourth generation, the dockless bike hire systems consist of a bicycle with a lock that is usually integrated onto the frame and does not require a docking station. The earliest versions of this system consisted of "for-rent-bicycles" that were locked with combination locks and that could be unlocked by a registered user by calling the vendor to receive the combination to unlock the bicycle. The user would then call the vendor a second time to communicate where the bicycle had been parked and locked. This system was further developed by Deutsche Bahn in 1998 to incorporate a digital authentication codes (that changes) to automatically lock and unlock bikes. Deutsche Bahn launched Call a Bike in 2000, enabling users to unlock via SMS or telephone call, and more recently with an app. Recent technological and operational improvements by telephones and GPSs have paved the way for dramatic increase of this type of private app driven "dockless" bicycle-sharing system. In particular in China, Ofo and Mobike have become the world's largest bike share operators with millions of bikes spread over 100 cities. Today dockless bike shares are designed whereby a user need not return the bike to a kiosk or station; rather, the next user can find it by GPS. Over 30 private companies have started operating in China. However, the rapid growth vastly outpaced immediate demand and overwhelmed Chinese cities, where infrastructure and regulations were not prepared to handle a sudden flood of millions of shared bicycles.