CHICAGO (CBS) — Chicago officials apologized Monday afternoon after some residents received an emergency alert on their phones about police activity.

The alert turned out to be a test that was distributed in error.

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The alert, issued around 3:30 p.m., read: “Test: CPD activity in your area. Remain indoors until further notice. Chicago OEMC.” Twitter users from around the city reported receiving the alert.

While many Twitter users assumed it was a test, others issued tweets of alarm or confusion.

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Late Monday afternoon, police and the Chicago Office of Emergency Management and Communications issued a tweet apologizing for the alert. The tweet said the message had been sent in error.

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