The Detroit Lions have signed cornerback Alphonso Smith and released running back Keiland Williams. The Lions are desperate for help at cornerback because Bill Bentley and Jacob Lacey missed Thursday's practice. Bentley was held out with a shoulder injury and Lacey because of a concussion. Smith was among the Lions' final cuts just before the season. The Lions, 2-3, play the Bears, 4-1, in Chicago Monday night.