Dockery and Harris are expected to give Pittsburgh's secondary some needed depth. Veterans Ike Taylor (broken thumb) and Bryant McFadden (hamstring) have been limited in training camp and neither will play Thursday when the Steelers host Philadelphia.
Dockery has four interceptions in five seasons and spent 2010 with the St. Louis Rams. Harris played with the Washington Redskins last season.
To make room for Dockery and Harris, the Steelers placed wide receiver Limas Sweed on the waived/injured list and waived tight end Eugene Bright.
Sweed, a second-round pick in the 2008, struggled during his three seasons in Pittsburgh. He missed the 2010 season completely after injuring his left Achilles tendon in minicamp.