Serena Williams Mistakes Drug Tester for Prowler reported that early last Wednesday morning at 6 a.m., Serena Williams locked herself in the “panic room” of her Los Angeles home when she thought there was an intruder.

Williams’ assistant called 911 and police came to investigate but left quickly when it was discovered that it was a misunderstanding.

The intruder was a  random drug tester who stopped by  for a urine sample. Tennis players are required to give urine samples in order to comply with tennis’ anti-doping policy.