(CHICAGO) Chicago Police are cautioning North Center residents after a pair of strong-arm robberies earlier this month.

About 10:15 p.m. on Oct. 2, four teens riding 10-speed bicycles rode up to a person in the 3200 block of North Campbell and demanded their cell phone, according to a community alert from Town Hall District detectives.

They were between 17 and 19 years old, and one of their bikes was neon green, police said.

A week later, they made off with more phones in a similar robbery in the 3400 block of North Rockwell, police said.

About 10:50 p.m. on Oct. 9, three robbers between 16 and 17 years old—one of them on a silver road bike—carried out the robbery in a park, police said.

Anyone with information should call Area North detectives at (312) 744-8263.