Oh those Germans. They can't let the French one-up them on anything, not even chess cheating. At the German championship last week, 23-year-old FM Christoph Natsidis of Bannewitz, who will now be quasi-famous for this one thing for the rest of his life thanks to Google and his own stupidity, decided it would be a good idea to check his position on his smartphone a few times in the toilet. ChessVibes has the story. (Repeated toilet trips, suspicious opponent.) Natsidis confessed and apologized when confronted, so I'm not sure we can even say he was caught. Had he stonewalled and refused to let the arbiter see his phone they probably would have had to disqualify him without further proof. I don't think anything has come out about Natsidis's other games -- he was on track for an IM norm and would have scored it even had he lost that final game.
But much the way refusing a breathalyzer test allows the state to do all sorts of things to you, the "consciousness of guilt evidence" (that is the term, as oxymoronic as it sounds) of his refusal to let them see his phone would have been strong, even if he could have denied guilt till death. I don't know if the German Ch actually has rules saying the arbiter has certain search powers that cannot be refused under penalty of disqualification, but apparently something like that is required. It will be interesting to see what the German federation will do. FIDE?!
I don't remember which of my chess tweeps said, regarding the event, that only top events can afford security. But while it would hardly be foolproof, you can get a hand-held security wand that will pick up a cell phone for less than a hundred bucks. Probably still not practical for big opens, but what would be? Lockers for checking phones are yet another expense and potential can of worms. The only thing you can do is give arbiters clear guidelines, limited powers, and make the penalties severe enough to create a deterrent. Stripping a player of his membership for a lengthy time first offense would be a good start. Second offense, chopping off a hand?