Alex had a gnawing, uneasy feeling when he boarded the last BART train from San Francisco International Airport, on the way home from a business trip in 2012. The station was dead empty. The 33-year-old risk-management consultant was alone, shuttling to a quiet East Bay suburb after midnight, dressed like the straight man in a noir movie. Alex wore a suit with slippery pockets. He slipped his iPhone4 into one of them, took a seat on the Pittsburg-Bay Point train, and crossed one leg over the other.

When he got off in Orinda, the phone was gone.

"It definitely just slipped out of my pocket on the BART train," Alex recalls. "I thought, 'Well, that was the last train, so it probably just went to the end of the line.'"

He went home, filled out a lost item form on BART's website, and sent a text message to his phone, offering a reward for whoever found it. He waited. Alex had one more option — "Find my iPhone," a new geo-locator app he'd installed at a time when few people knew such safeguards existed. The app would signal Apple as soon as anyone plugged the pilfered phone into a wall socket to juice the battery.

And so, after a couple days of science, Alex received an email from Apple, indicating that his iPhone's location had been recorded.

Alex was emboldened. "I wanted my phone back," he says. "You know how much those things cost, without a contract?" In 2012, an iPhone 4 would have cost $549 without a contract; the most current model, an iPhone 5S, would cost $849 today.

But Alex was fairly certain he could turn up the lost device. By logging into his Apple iCloud account, he was able to access the geo-tracking feature and determine that the phone was languishing somewhere in Clayton, a small bedroom community at the foot of Mount Diablo. "My immediate reaction was, 'Okay, this is either wrong, or some asshole stole my phone and took it home."

He sent a few more texts. The phone stayed offline for a couple days, then showed up again on his iCloud account, beaming signals from the same spot, in Clayton. Alex was infuriated. He could tell someone had read the messages, ignored them, and charged the phone anyway.

He got on Google Maps and scoped out the area: upscale colonial houses, manicured lawns, BMWs parked in driveways. He traced the phone to an address, then tied that address to a couple kids who attended a nearby school. Then, through a little more sleuthing, he found the name of the homeowner. "By the time I was done," Alex says, "I knew the names of his kids and how much his mortgage payment was. I just needed a home number."

That, and a little assistance from the companies who'd sold him the phone and yoked it to an ironclad service contract. But none was forthcoming.

Alex called AT&T, said he'd figured out who'd stolen his phone, and asked if the company could help get it back — perhaps by flagging the phone if the thief tried to register it in a new name. No dice. AT&T gave him two options: Either deactivate the phone and buy a new one, or find a cop willing to subpoena AT&T for information, file a lengthy police report, and go through a long bureaucratic process.

It was, Alex says, "the most B.S. story I've ever heard."

He called Apple and was invited to try the same "find my phone" app he'd already been using.

Alex realized that if he wanted the phone back, he'd have to get it himself. He got in his car and headed to Clayton.

It turns out the dismissive responses that Alex received in his quest to find the stolen iPhone were typical of telecom companies and service carriers. Apple and AT&T have little reason to help someone recover a device — even if it's within reach. Smartphone theft is a lucrative business, and not just for the small-time crooks who lift gadgets off of BART seats. The manufacturer profits by hawking a replacement phone; the carrier profits double, by locking the crime victim into a new contract, then opening an account with whomever ends up with the stolen phone. Telecom companies even profit from the specter of phone theft, by selling expensive insurance policies to protect their users.

"We've tried to blow the whistle on this for years," Capt. Jason Cherniss of the San Francisco Police Department says. "And these companies have had the ability to prevent it for years." In the meantime, he adds, people have been violently robbed — even killed — and millions of dollars have changed hands on the black market.

Alex would quickly find out that the entire smartphone industry functions as a protection racket. And culpability doesn't just lie with the unhelpful customer service representatives.

When Alex arrived in Clayton, he canvassed the neighborhood until he spotted the house where his iPhone was now living. He knocked on the door. A woman answered, regarding Alex with a look of polite concern. He told her that he'd lost his phone on BART, and Apple had traced it to his address.

"Oh, you should talk to my husband," the woman said. "He works for BART."

She summoned a man whose face resembled photographs Alex had uncovered doing property searches. He was Victor du Long: suburban homeowner, family man, BART cop. Du Long gingerly addressed Alex, clutching the purloined phone in one hand. Even then, the officer seemed like an improbable culprit.

Smartphone theft is the consummate crime of opportunity, particularly in a society saturated by modern gadgetry. Glance up the next time you're riding a BART train or sitting in the back of a Muni bus: Dozens of screens aglow as scores of thumbs peck at tiny keyboards. We obsessively check email and plink tech messages to friends; we walk down busy retail corridors with phones clasped to our ears or dangling from our palms. If you're a thief looking to make a quick payday, this city's downtown streets are your oyster.