The driver of a Tesla Model S has told how he became stranded outside Las Vegas when the app that doubles as a key fob stopped working because it lost signal.The Telegraph reports that Ryan Negri got out of his car in the Red Rock Canyon area and when he went to get back in, the phone wasn't connected so the car wouldn't open.His wife had to run two miles to get a signal and phone a friend to bring a set of keys.The keyless smartphone feature, which is available through Tesla's iPhone and Android apps, lets users remotely monitor and control their Tesla Model S without their key.  One of the main features of the app is the ability to "unlock and drive Model S without your key".The Telegraph adds that because smartphone car control is still a fairly new concept and that Negri said he should have taken his keys as a precaution but also criticised Tesla for not having a contingency plan in such cases.(Picture - Ryan Negri's Instagram feed)