In four Monterrey churches, Israeli-made cell phone jammers the size of paperbacks have been tucked unobtrusively among paintings of the Madonna and statues of the saints.
The jarring polychromatic din of ringing cell phones is increasingly being thwarted - from religious sanctuaries to India's parliament to Tokyo theaters and commuter trains - by devices originally developed to help security forces avert eavesdropping and thwart phone-triggered bombings.
The Indian parliament had jammers installed after politicians ignored requests to turn off their cell phones and legislative sessions were constantly interrupted.
In Italy, universities started using the blockers after discovering that cell phone-savvy teenagers were cheating on exams by sending text messages or taking pictures of tests.
The four Roman Catholic Churches in this northern city began using the devices, from Tel Aviv-based Netline Communications Technologies Ltd., after an insurance salesman imported them as a personal favor for a priest.
"There are still many people who don't understand that being at Mass is sharing a moment with God," said the Rev. Juan Jose Martinez, a spokesman for archdiocese. "Sadly, we had no other choice but to use these little gadgets."
Purchased for about $2,000 each, they can be turned on by remote control and emit low-level radio frequencies that thwart cell phone signals within a 100-foot radius.
Users get a "no service" or "signal not available" message on their cell phones.
Although Mexico has no law against the devices, the private use of cell phone blockers is illegal in the United States and most Western countries.
But the tide is turning.
Japan allows public places such as theaters and concert halls to install jammers, provided they obtain a government-issued license. And last week, France's industry minister approved a decision to let cinemas, concert halls and theaters install them - as long as provisions are in place so emergency calls can still be made.
Canada had considered allowing blocking in similar situations. But Industry Canada, which regulates the country's telecommunications, decided against it, saying the devices could infringe on personal freedom and affect public safety by crippling communication with law enforcement and security agencies.
Officials at Netline, which sold its first jammer in 1998, say they are selling thousands of jammers a year and have expanded their business throughout the world.
They're far from the only manufacturers. The devices are sold the world over, with dozens of suppliers selling them on the Internet.
Tokyo-based Medic Inc. sold thousands of its Wave Wall jammers before the government stepped in and regulated their use to venues with live performances. Commuters still buy mobile jammers to shut up chatty train passengers, even though their use is illegal.
In Scotland, businessman Ronnie McGuire, owner of Electron Electrical Engineering Services, imported Taiwan-made cell phone blockers and sold them to hotels, restaurants and bars until a local newspaper reported his activities, which were illegal in Britain.
McGuire has said he will still import the Taiwanese devices but sell them for export only to countries where they are allowed.
Loreen Haim, the director of marketing and sales for Netline, wouldn't say how many devices the company sells per year or what country buys the most.
In Mexico, the main clients have been banks looking to stop would-be robbers from communicating with their accomplices and the Mexican government, which is planning to use them at prisons, Haim said.
In Monterrey, the Sacred Heart church, a baroque temple favored by Mexico's elite for weddings, church officials acquired their blockers two years ago.
"Whenever there was a wedding, cell phones would ring every five minutes," said Bulmaro Carranza, a parish clerk. "It was a real problem because there were times when even the groom would forget to turn his cell phone off."
For months, the devices went unnoticed until reporters covering the weddings began complaining that their cell phones never worked.
Since word of the jammers went public, priests from around Mexico have been calling to find out how to get them, said Carranza.
At Sacred Heart, a device at the entrance to the church and another by the altar are turned on right before every Mass. Still, priests remind parishioners to turn off their phones before beginning the services, hoping good cell phone etiquette will eventually catch on.
The other Monterrey churches with the devices - The Rosario, San Juan Bosco and Our Lady Queen of the Angels - are also frequented by wealthier parishioners, Martinez said.
"For a lot of them, the cell phone is a necessity. But that shouldn't prevent them from having good manners and remembering that one must respect sacred places," Martinez said.
Margarita Escobedo, a Catholic who goes to church at least twice a week and volunteers at the San Genaro church, says she would welcome the jammers in her parish, where cell phones are becoming a nuisance.
"Those who bring cell phones to church are not committed to God," Escobedo said. "It's very distracting to be praying and suddenly hear birds chirping or techno music."
By Olga R. Rodriguez