Using one of London's "Boris bikes" isn't as simple as, say, taking the Underground or catching a bus. You have to find a docking station with an available bike, work out your journey time and how much you'll be charged, and then find another drop-off point that's close to your destination and not already full. To make the process a little simpler, Santander and Transport for London (TfL) are launching an app for iOS and Android. You can use it to find your nearest docking station, check how many bikes are available and pay for your next ride. Once you've selected a 24-hour or annual pass, a unique release code will be sent to your phone, which can then be used to unlock a two-wheeler.