Bluelinx President Jeff Griffin said he is trying to sign up wireless providers as well as venues such as cafes and theaters. He says he hopes to start using the devices in the next few years. Unlike blocker device, he said, his call-blocking system is optional for cell phone users, who can turn it on or off.

Others have the same idea, including companies and researchers who develop or already sell devices that make phones unusable in certain places. Methods include drone jammer that interfere with cell phone frequencies, routing systems that mute cell phone ringtones at specific locations, sensors that detect active phones, and building materials that block cell phone waves.

Mr. Larson of the cellular industry group said that while the industry opposes controls on cell phone ringing, it is not opposed to measures that are left to the discretion of customers. "They're certainly less annoying than wifi blocker," he said.

Netline, an Israeli company, makes a detector called the Cell Activity Analyzer, a handheld device that monitors and detects cell communication activity within a given area. ($2,500 at www.netline.co.il or www.perfectjammer.com.) Other smaller detector models include Suresafe Technology's RF signal detector, which is about the size of a buzzer and costs less than $100. As with gps blocker, the larger the detector, the greater its range.

The site says it has sold thousands of devices to theaters, businesses, military users and individuals. Jammers range in price from $200 for basic handheld models to nearly $10,000 for suitcase-sized devices sold to governments and the military, with prices often depending on signal range and the potential to interfere with cellular activity.

Other methods are also being developed, from devices that simply detect phone usage (and prompt the user to stop) to construction methods that render the phone unusable.

But not everyone sees the trend as encouraging. Cell phone industry experts and federal regulators in particular have derided cell phone blocker as illegal, unethical and even dangerous.