The first robbery occurred on the 3600 block of West Avenue K-15 at around 10 p.m.
Investigators say two armed men in ski masks kicked in the front door of a home and identified themselves as the sheriff's department.
One person inside was able to call 911. The men then fled.
About an hour-and-a-half later, authorities were called to the 5700 block of Spice Street following a similar robbery.
Only this time, the would-be robbers were confronted by a retired detective who had a gun of his own and fired two shots. In this instance, the men were also able to flee. It appears neither of the suspects was struck by gunfire.
The suspects were described as two African-American males.
Anyone with information about the robberies was asked to call Lancaster Sheriff's Station Robbery/Assault Detective Sergeant Eric Roelofson at (661) 948-8466.