Can the jammer penetrate other adjacent frequency bands?

NEW YORK – A cafe customer, fed up with cellphone chatter, sits in a bubble of blissful silence as nearby guests puzzle over dead cellphones.

A man tries to take a secret snapshot with his camera phone, but only gets a blank screen.

A priest gives his church a new energy – the electromagnetic way – to keep his sermons calm and free from beeps, chirps and rocking ringtones.

These are glimpses of a war of gadgets that play quietly around the world.

While millions embrace the freedom of mobile communication, some people and companies are pushing against the current. They fight technology with technology, use detectors, signal jammer, and other things to protect privacy, security, and sometimes reason.

Cell phone interference is illegal in the United States, but since foreign companies and even eBay sell pocket-sized online devices on the Internet and the military and government are already using such devices, the wireless struggle is already here.

“It’s like the battle between the radar detector and the radar cannons. It keeps escalating,” said Jeff Kagan, an independent Atlanta-based telecommunications analyst. He said the need for such devices was triggered by the “double-edged sword of technology”.

“The inventor of the cell phone never thought that people would use it all the time and would affect other people’s privacy,” he said. “The inventor of the camera phone never thought about being used in locker rooms and other unsuitable places.”

Interfering with a cell phone, essentially a walkie-talkie, is relatively straightforward.

Jammers typically interrupt communication between handsets and cell towers by flooding an area with interference or selectively blocking signals by transmitting on the same frequencies that the phones use.

Some jammers may need to be as smart as a cell phone trying to increase performance or hop to other radio channels to avoid interference.

Depending on their strength, jammers can interfere with communication in a range of a few meters or several kilometers.

Commercial jammers have been sold overseas for years, and some internet bookings even include instructions for making homemade models.

However, FCC officials say they have received very few complaints about jammed cell phones and have never acted against anyone for the injury.

The jammer industry says that individuals use low-power devices with little fear of reprisals because it is difficult, if not impossible, for a caller to distinguish between a blocked signal and a normal area of ​​the cell phone.

Even so, U.S. law discourages the use of jammers and limits its distribution to consumers, analyst Kagan said.

Larson said to reduce annoyance when using cell phones, customers should use “mute button, volume control, vibration mode, voicemail, and an on-off switch” when needed.

He said congestion in a certain area where silence is expected, such as a movie theater, is still a risk even with warning signs.

“Jammers can penetrate other neighboring frequency bands and block public safety radio signals used by police officers and firefighters,” he said.

But safety concerns, courtesy suggestions, and the law didn’t stop people from buying jammers.

British company Global Gadget UK sells a range of interference and detection products to people in other countries, including a portable jammer disguised as a cell phone that can disrupt cellular communications up to 10 meters away from the user.