Other than that, I might not exist here in Andalusia, digitally speaking. The last my credit card company knew, I was in Heathrow eating a sandwich. Iberia knows we're booked back to London the day after tomorrow, but it has no idea where we are. I have, largely, slipped my data chains.

The wedding, under a high azure sky, begins at noon the next day and—in epic Spanish fashion—lasts for seventeen hours, as my daughter Eliza clocks it. At four in the morning, I am identified not by name but with the sobriquet Señor Cerveza by a fellow party guest at the bar. I won't elaborate on his claim, but the party had just mysteriously run out of beer.

The banks catch up with me as I pay the room service tab upon checkout, but their real-time knowledge of my whereabouts is good only for the ninety seconds before we jump in the cab and peel out for the airport. As we leave Spain, there is again no watch list—just a stamp and we're gone.

Although the British Isles are nominally in the EU, there is no laissez-faire at U.K. borders, no matter where you're from. We're asked to state the nature of our visit, how long we're staying, and where. Her Majesty's government now has the hotel—the Mandarin Oriental in Knightsbridge. They know I'm here for a week on business, that my wife and daughter are heading back to the States shortly. As he interviews me, the U.K. immigration officer puts my passport number and name through watch lists supplied to his agency by a variety of heavy-hitting sources: among them, Interpol, MI5 (the British counterintelligence agency), and the intelligence agencies of allied countries.

The Mandarin Oriental, the towering Victorian icon of Knightsbridge, has my credit card information, home address, passport number, corporate affiliation—roughly the same coordinates of identity that the airlines have. But the hotel has something else, too, namely my body.

The better hotels discreetly monitor their guests. Their interest is to fix an identity that they can know and serve. It's the nexus of hospitality and intelligence-gathering. Observant hotel staff know how often you're in the room (and usually with whom), how much you talk on the telephone, what you eat, what and how much you drink, whether you like pay-per-view porn. Unless it's a hotel in, say, Pyongyang, North Korea, they don't abuse the knowledge.

"Within twenty-four hours of your arrival, we want staff to be using your name," says Chris Holtby, a brawny former London police officer, head of security at the Mandarin Oriental hotel for the last three years. "We want you to tap into a network of people who are getting to know you."

As part of their getting to know me, I later learn, the hotel also has a digital image of me, captured surreptitiously at reception. "We mean to do it," explains Holtby, "but we don't want the guest to feel observed. We have eighty closed-circuit TV cameras in the public areas of the hotel, most of them covert. I'm very flattered when the guests tell me that they haven't noticed any cameras, since my job is to secure the hotel but to keep the lowest profile we can."