Which is why they have this nifty device called a cell phone jammer. It emits radio frequencies that confuse and "jam" the signal of whatever is broadcasting a signal. Local pervs would probably only have the personal device (reaches about 5-10 meters). Professionals, however, have military grade jammers that reach up to 800 meters. They also take the victim to a separate, disclosed location (such as a wooded area or abandoned warehouse) where they remove the device.

I'm just saying that the potential side-effects, effectiveness (or lack thereof), invasion of privacy, and misuse of these devices outweigh the extremely rare cases of where they may help.