Police said it happened around 9:30 a.m. at a home on Tweed Circle in the MacGregor Downs neighborhood.
The victim - who asked not to be identified - told ABC11 he had just dropped his grandson off at school and came home to find the man waiting inside.
Police said the man left his garage door open while he made the trip.
"This appears to have been a crime of opportunity, resulting from the suspect seeing the open garage door," said Cary Police Department District 3 Captain Randall Rhyne. "We can’t stress enough the importance of citizens locking their vehicles and closing their garage doors after them when they enter their homes."
The victim was held at gunpoint and tied to a bed. The robber then took off with his wallet and Cadillac STS.
The victim was able to free himself and call for help.
Police caught up with the alleged robber in Johnston County. Twenty-six-year-old James Deetz is now charged with felony breaking and entering, kidnapping, robbery with a dangerous weapon, and larceny of a motor vehicle.