SAN FRANCISCO (CBS SF) — San Francisco Police are adding extra patrols after burglars smashed through another store front before making off with merchandise.

Three men shattered the front window of Music Lovers electronics store in Pacific Heights around 4 a.m. Wednesday morning.

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One witness said the suspects faces were covered with bandanas as they stole speakers from the store.

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There have been at least six similar thefts in San Francisco over the past month.  Electronic shop owners say they’re watching each other’s backs.

“They are keeping an eye on each other, and other ways to safeguard their inventory,” SFPD Sergeant Dean Marcic said.

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Police say there are similarities between all the burglaries, and that the suspects are experienced.