Montgomery County police are advising older residents to lock down their homes after a Chevy Chase couple in their 70s were tied up and robbed early Wednesday morning, a home invasion police believe may be linked to four others in the past eight months.

The couple, who live on the 5800 block of Brookside Drive in the upper-class Kensington neighborhood, were awakened around 2:30 a.m. by a man between 20 and 30 years old, 5 feet 8 inches tall and about 150 pounds, Montgomery County police said. The man, who was carrying a handgun, tied them up and demanded valuables. He spent aboutan hour rummaging through the house, at one point striking the female victim, and fled with an unknown number of items. The woman’s injuries were reported as minor.