If you live in Arlington, police have a message for you: Lock up your bike. Bicycle theft in the county is at an all-time high, according to police statistics.

Sixty-seven bikes were stolen in July, 21 more than in any other month in the past three years, police said. From June 1 to Aug. 5, 126 bikes were reported stolen, an estimated property loss of nearly $100,000.

Arlington police officials generally like to emphasize that crime in the county is low. But when it comes to their bikes, some residents might feel a little too safe. People are leaving bikes in garages and storage spaces and on balconies and patios without any locks at all, or locking them outside with cables that are easy to cut, police spokesman Dustin Sternbeck said.

“The ultimate goal is to get residents to pay a little bit more attention,” Sternbeck said.

Police are conducting extra patrols and surveillance to address the spike. Six people tied to multiple bike thefts have been arrested. Michael Cullen, 42, pleaded guilty this week to nine felony counts for stealing bicycles.

But, Sternbeck said, “it’s also a team effort.”

The police are encouraging residents to register their bicycles, which makes them easier to track. They recommend using U-locks at all times.

Clarendon is the hottest spot in Arlington for bike thievery, according to police, and Trek bikes are the brand stolen most often.

The warning comes as Metro officials report that thefts of smartphones and other electronic devices on the transit system also have spiked.