Santa is not real. But Twitter is, and it knows when you are sleeping.

Twitter knows when you nap. At least its engineers think they have a pretty good idea when you nap, because those are the few times when you’re not pouring your heart out in 140-character bursts.

Peering into its fire hose of tweets from four big cities around the world, a pair of Twitter engineers, Miguel Rios and Jimmy Lin, have discovered that the Twitter users in Istanbul don’t sleep much in August — and why would they, considering how many people are strolling along Istiklal Avenue on summer evenings. The denizens of Sao Paulo, Brazil, seem to take an afternoon siesta – tweets sharply drop off in the period after lunch.

New Yorkers tend to be as voluble on Twitter during the workday as they are during evenings. But that is not the case for the other three cities. The Japanese in Tokyo appear to be most disciplined about actually working during work hours – they tweet very little, relatively speaking, between 10 a.m. and 6 p.m. Their sleeping hours also appear relatively unchanged over winter and summer.

The Times totally riffs on my Santa Clause meme with respect to Acxiom:

 IT knows who you are. It knows where you live. It knows what you do.

It peers deeper into American life than the F.B.I. or the I.R.S., or those prying digital eyes at Facebook and Google. If you are an American adult, the odds are that it knows things like your age, race, sex, weight, height, marital status, education level, politics, buying habits, household health worries, vacation dreams — and on and on.

Right now in Conway, Ark., north of Little Rock, more than 23,000 computer servers are collecting, collating and analyzing consumer data for a company that, unlike Silicon Valley’s marquee names, rarely makes headlines. It’s called the Acxiom Corporation, and it’s the quiet giant of a multibillion-dollar industry known as database marketing.