The way corrections officers tell it, a smuggled cell phone can be more dangerous than a weapon behind bars. A burner hidden in a hollowed out Bible could be used to coordinate gang attacks, or to send threatening messages to victims on the outside. Problem is, communications technology is moving faster than the technology to block it.

The Associated Press reports that California is pausing a four-year-old program to prevent unauthorized cell phone signals from penetrating prison walls because the state can’t tell whether the calls can be effectively blocked. Global Tel-Link, a prison phone company, was installing the service free of charge on the hopes it would help push inmates towards using its authorized phones, thereby giving Global Tel-Link a monopoly on the lucrative corrections’ phone bills. The FCC capped call rates this October, but until recently a prison phone company soaked people for as much as $14 a minute for an in-state call, with much of the billing sent to struggling families.

Global Tel-Link’s blocking system made it into 18 of the state’s 34 prisons, and for now that seems as far as it’ll go, because cell phone companies of 2015 are using drastically different networks than the companies of 2011. Between 4G and Long Term Evolution services, phone companies are transmitting calls over a system that has more in common with a wifi network than old-school cell connections.

It seems incredibly simple to smuggle a phone in — even Charles Manson was busted not once but twice with mobile under the mattress. In the absence of effective prevention, blocking technology has become big business. The annual conference of the National Sheriffs’ Association in June was filled with companies either promising to block signals or, like Cellsense, trying to sell corrections departments on a 7-foot phone-detecting wand that could sniff out a Samsung concealed in the most sensitive crevices of the human body. You can bet as you read this some startup is working on a way to harness these illicit messages once and for all, and whoever masters it is probably going to make a lot of money doing it. Actually finding ways for inmates to communicate cheaply and effectively with their loved ones is decidedly less lucrative.