On Kawara is a Japanese conceptual artist. On each day, between 1968 and 1979, he would send two different friends or colleagues a picture postcard, stamped with the exact time he arose that day and the addresses of both sender and recipient. This work was called I GOT UP.
The message on the postcard was always the same: “I GOT UP.” The only variables in this otherwise monomaniacal work were the postcard and the specific time and place of On Kawara’s waking. In a sense, he started Tweeting two decades before the advent of internet – each ‘Tweet’ containing the fundamental message that every Tweet contains: I communicate that I exist. In On Kawara’s case: I communicate that I exist in a given time and place.
By the way, check out On Kawara’s Twitter account.