Celebrities may be accustomed to the presence of flashing camera bulbs outside their Hollywood digs, but now thanks to a disturbing new trend, they’re also growing familiar with the sight of flashing police lights.

The stunt is known as ‘swatting,’ in which a call is placed to 911 reporting a bogus crime. The false report prompts police and other first responders to make an emergency run. Depending on the severity of the violence being reported, they may arrive at a location fully armed.

The incidents have been happening a lot in the U.S., and now in Hollywood, where celebrities have become favoured targets.

On Friday, a group of tourists in the Hollywood Hills watched drama unfold outside the home of Justin Timberlake when a Special Weapons and Tactics (SWAT) team descended on the superstar’s home to investigate a fake call about gunfire.

Hours later, authorities arrived at Selena Gomez’s doorstep after receiving a 911 call regarding gunfire inside her estate. The actor-singer was reportedly at home with her mother when police arrived.

Gomez and Timberlake join a growing list of celebrities who have been targets of swatting: Rihanna, Justin Bieber, Tom Cruise and Clint Eastwood have all been victims.

In October, several of actor Ashton Kutcher’s household staff members were forced out of the actor’s home at police gunpoint after authorities received a call about a home invasion. They later determined it was a hoax.

A 12-year-old boy later admitted to making a false bomb threat, The Associated Press reported in March.

As per protocol, authorities must be dispatched to the area if a 911 call is made. Emergency responders must assume every call is real.

The frequency with which the incidents are occurring is beginning to frustrate the Los Angeles Police Department. The incidents are costly for the police resources and could pose a deadly threat, if there was to be even a small misunderstanding.

“The residents that we are responding to -- they may not have any idea that we are responding to their home,” said Officer Sara Faden, of the Los Angeles Police Department. “It can be pretty scary.”

Experts say upgraded police technology, including Global Positioning Systems may help authorities pinpoint where the bogus calls are being placed, so officers are able to crackdown on the criminal activity.