Serena Williams Panic Room False Alarm

Law enforcement sources tell TMZ, Serena's assistant called 911 around 6AM last Wednesday, reporting a possible burglar or prowler. It was so serious, we're told Serena retreated to her panic room for safe keeping in case things got dangerous.

But we're told, it was a false alarm -- the person on Serena's security camera was a random drug tester for an unspecified tennis association, stopping by Serena's pad unannounced for some pee.