I headed to the office, pondering the potential damage. The phone has a pass code to prevent just anyone from picking it up and using it, but I assumed a skilled thief could defeat that. What sort of personal information was on the device? Lots. What else was important about the 2-year-old phone? Well, maybe not much. But I use its camera a lot and reflected sadly on the very last shot I had taken, just before I'd gotten on the train to the city.

At work, I went online to see if the iPhone finder app would actually tell me anything about the phone's whereabouts. I was pleasantly surprised to see the phone's location popped up immediately: It had traveled down the BART line a few stops, then accompanied some stranger to a residence in Daly City.

Now, the app lets you send a contact number and text message to whomever might have the phone, whether well-meaning stranger or light-fingered ne'er-do-well. I sent my office phone number and a message first thing. The app also allows you to turn on a loud, ringing pulse from the lost device. I activated that. The app offers a third option: Erase iPhone. If you know the phone has been stolen, hit that and, in theory, you can wipe your personal information from the device.

Nothing happened when I sent the phone number and message. The app had pinpointed the phone at a specific address. I street-viewed the location on Google Maps, then tried a reverse directory search to see if there was a phone number associated with the address. No — no phones or residents listed at the house.

And right around here, after the phone had been out of my possession for an hour or so and I could see where it was supposed to be and no one was responding to my message or repeated pings, I started to get a little obsessive. I sent a second message mentioning I knew what block the phone was on. I sent more pings. I sent a message offering a reward. I sent more pings. I looked at Street View again. Then more pings and more Street View. Damn! The phone wasn't moving. Why didn't whoever had it call?

I thought about calling the police, remembering an incident in Berkeley in which the chief had sent 10 officers looking for his son's lost iPhone. I also recalled an episode in which a neighbor had used Find My iPhone to track and retrieve a stolen iPad. But I didn't call the police because I wasn't really sure my phone was stolen and it felt a little weird to enlist the cops for my own personal lost-and-found detail.

I thought about erasing the iPhone. When I opened the window to do that, though, the app warned I would no longer be able to track the device if I proceeded. That felt too final, and part of me still held out hope that a kindhearted, soon-to-be-revealed good Samaritan would deliver the phone into my hands.

I was thinking about borrowing a car and driving down to Daly City when suddenly the map showed the phone moving. First, it got on Interstate 280 and headed north. When it got to U.S. 101, it headed north again. The phone stopped just off the freeway in the Bayview District for 10 or 15 minutes. Google showed the location to be a storage warehouse, so I wondered whether my phone was about to be added to a bin of hundreds of lost or stolen mobile devices. I filed an online lost property report with the San Francisco police and waited further developments.

Whoa. The phone was moving again. Up to San Francisco General Hospital, just a half-mile from my office. Maybe some tech-savvy, kindhearted good Samaritan had figured out where I worked and was bringing it to me! I sent a message saying I was in the neighborhood if the Samaritan wanted to drop by.

But no. The phone headed in the opposite direction, up over Potrero Hill. It made a feint toward my office — Is the kindhearted Samaritan lost? — then traveled at public-transit speed north to the Caltrain Station at Fourth and Townsend, through SoMa, across the Financial District to North Beach and the edge of Chinatown. And there it came to an extended stop again.

I sent a couple more pings and another text during this odyssey and after I saw it had stopped. Still no answer.

I had insisted on updating coworkers on this drama's minute-by-minute progress all afternoon. By this time, after 5 o'clock, most had voiced the reasonable opinion that the lack of response over several hours meant that whoever had happened upon the phone had no intention of returning it. I suspected they were right, but I also could picture the finder throwing it into a purse or backpack and forgetting about it. When I said that out loud, one office-mate shook her head and commented on my surprising faith in humanity.

It's true I wasn't necessarily thinking the worst about whoever was carrying the phone, but this wasn't really faith. I was able to see where the phone was. But as long as the unseen finder remained silent, the phone was just as gone as those five-dollar bills I was in the habit of losing as a kid. So my messages started reasonably enough as a simple return request, then progressed from implied threat to promise to cajolery to resignation.

Finally, I had drawn out the workday about as far as it would go. I was noodling around with a couple of things and getting ready to leave work, and abandon my poor lonely iPhone in the city, when my desk line rang. I answered. "My boyfriend found your phone and would like to return it," a woman said. "Well, I'd love to have it back," I answered. The woman, who said her name was Andrea, gave me an address — it matched the location the phone-finder app gave — and told me her boyfriend, Danny, would be there when I arrived.

A coworker dropped me off in North Beach, I stopped at an ATM to get some cash, and then I went to the address on Pacific Avenue, a run-down city-owned apartment block. It was dark by this time.

I made my way up to the open-air second-floor corridor and found the apartment number I was looking for. The passageway was lined with containers full of empty bottles and cans to be recycled. The venetian blinds on the windows were broken and askew. I knocked on the door. No one came. I left to check whether I was at the right address. Yeah, I was. I went back upstairs and knocked again. Again no answer. I knocked louder. After 15 or 20 seconds, a lock turned and the door opened.

"You're Danny?" I asked. "Yeah, that's right." he said. "I guess you don't have to go and buy a new phone." He said it twice and handed me the phone.

I shook his hand and took out my wallet, removed a twenty and gave it to him. "I wanted to give you something," I said. "Wish it was more." I looked past him into the apartment, where there seemed to be a floor-to-ceiling pile of, well, stuff.

He closed the door behind him. "That's OK," he said. "That's OK."

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Finding My Lost iPhone: A Story of Apps, Obsession and a Good Samaritan