"I just wanted to see what it was like getting in here," Obama said. "I think I beeped a couple of times."
Obama shook hands with gatehouse guards at the Northwest Gate and talked football as he returned to the White House from a holiday party with National Security Council staff across Pennsylvania Avenue at Blair House.
As Obama walked through the metal detector, it went off. A guard told him his cellphone probably was the culprit.
Earlier, former U.S. Sen. Christopher Dodd, D-Conn., was spotted emerging from the White House.
Obama declined to answer shouted questions about the latest Republican tax cut bill.