FLORHAM PARK, N.J. — Police in Florham Park, N.J., are warning residents that robbers may be using Wi-Fi jammers to prevent victims from using their cell phones to call for help.

Floham Park Police are investigating an attempted robbery involving a Wi-Fi jammer

A Florham Park resident was in his basement around 11:30 a.m. Monday when he heard a loud bang from the first floor, police said. When he checked his home security footage, he saw a stranger trying to enter his home.

The man then lost service on his camera system and cell phone, according to police.

Police believe the suspect used a Wi-Fi jammer — a device about the size of a smartphone that disables devices that use the signal.

Police said the suspect ran away, and the victim, still unable to use his phone, ran outside and flagged down a pedestrian who helped him call 911. Officers arrived shortly after, but police said the suspect had already fled.

"The victim had enough time to leave the area between the time he stepped outside and the time he flagged down a passerby and had him call the police," said Lt. Brian Ford of the Florham Park Police Department.

WiFi signal jammers can even block signals from police intercoms, home alarm systems and surveillance cameras that connect via Wi-Fi. The devices are illegal under federal law, and state Rep. Carol Murphy introduced legislation earlier this year to criminalize them at the state level.

"Every time I see something like this, I think, 'Wow, I need my law to pass,' because it's about giving law enforcement the resources to do what they have to do. I never want to see a story like this again," Murphy said.

"While Wi-Fi jammers are nothing new to criminals, this is the first time we've seen or heard of them being used in Morris County," Florham Park Police Chief Joseph Orlando said in a statement.

No arrests have been made.

Attempted robbery victim in New Jersey has no recourse

The Florham Park Police Department may be linking the incident to a theft ring known as the "South American Theft Syndicate."

According to police, they usually work in groups of three and install hidden cameras in the landscape to track the movements of potential victims.

Police recommend that if you can, you should change your daily routine, check and report any suspicious devices and cars inside and outside the house, and even install wired security cameras and landlines.