alt Hacker NewsYou could also open your front door with your smart phone. It would look high tech until your battery is empty.
Sometimes I see people captured by the train station unable to check out. They usually find someone with a charger but technically the formula is to fine them for not having a ticket. Then one might still need to buy a ticket to continue the journey. (bring cash)
Phones are usually empty when things [already] aren't going as planned.
Back in my iPhone days, I once got bitten by a bug where the app developer failed to raise that flag "dear OS, I'm in the middle of presenting a ticket for optical scanning, and it would be really amazing if you could just, you know, not disturb the screen with random shit for a couple seconds."
Unfortunately for me though, the turnstile that I was about to pass to exit the train station had both an optical scanner and some NFC thing lumped into the same physical module, and every time I tried to scan my ticket, the phone would raise its NFC screen and hide the 2D matrix code.
So yes, you can have a fully charged phone and a perfectly valid ticket with the latest software and still get stuck in a train station.