Cell phone jammers are devices that can jam mobile phone signals within a certain range. This is effective in creating a privacy bubble prohibiting any one to use a cell phone within that range. The device achieves this by emitting a frequency same as mobile connectivity, thereby creating a strong interference. The mobile user would receive the common notification of weak signal reception and would not be able to make or receive calls in the jamming sphere. Unless the user is aware of the presence of the jammer, he/she would recognize this as a usual signal fail, which is a general issue with all mobile carriers.
However, not everyone can use such a device without authority permission. Its size may vary from being a small cell phone like device to something as big as a briefcase. The range of dead space varies from a radius of about 100 feet (30 meters) to up to 1 mile (1.6 km). In the US, the FCC (Federal Communication Commission) holds unauthorized signal jamming as a type of property theft. However, the FCC also does not hold anyone accountable for manufacturing and selling the device. Military, law enforcement, and other government agencies often use these for various purposes. Using a powerful jamming device in the presidential motorcade is a common security protocol to disarm terrorists from using cell phones as an explosive trigger.