Chris Brown has cops on high alert these days ... and an anonymous tip that the passenger in his car had a gun was enough for L.A.'s finest to spring into action.
Law enforcement sources tell TMZ ... the LAPD got a call from someone saying Chris' passenger was carrying a gun. Chris was already inside Sayer nightclub in Hollywood, but the cops were able to coral the friend, detain him and search Chris' Lambo. They found nothing.
Chris was attending TI's pre-Grammy party when it went down. Cops are well aware trouble sometimes finds him. You'll recall he was performing at a VMA party at 1OAK last Summer when shots rang out and Suge Knight was hit 6 times. Last month 5 people were shot when Brown was performing in San Jose.
On the bright side, Brown tweeted Friday he's completed his community service in the Rihanna case.