Since jamming on the hardware level is out of the question, a number of developers have found a way to clog up WiFi communications in software. This is much more akin to a denial of service attack, where tools are used to repeatedly spam deauthentication packets at WiFi access points and clients to force them to disconnect. With the appropriate software and a powerful WiFi adapter that supports packet injection, an attacker can put a stranglehold on legitimate communications.
To be very clear, calling this technique jamming is inaccurate, but that hasn’t stopped a number of developers from using the term, so we’ll just play along for the sake of consistency. To properly jam WiFi (or any other form of radio communication), you basically blast out a lot of random noises on the frequencies that particular technology uses. It’s conceptually very simple, but also a very big infraction as far as our friends at the Federal Communications Commission are concerned; so it isn’t something you won’t be doing with any consumer-level WiFi hardware.
Networks can be signal jammer by flooding the AP with Deauthentication Frames in what is know as a deauth-attack. By assuming the identity (MAC address) of a station on the network, the AP will deauthenticate the real station. The real station will then attempt to reauthenticate, but, it will never succeed due to our barrage of deauth-frames and its network access will be effectively blocked.
To jam a cell phone, you need a device that broadcasts on the correct frequencies. Although different cellular systems process signals differently, all cell-phone networks use radio signals that can be interrupted. GSM, used in digital cellular and PCS-based systems, operates in the 900-MHz and 1800-MHz bands in Europe and Asia and in the 1900-MHz band in the United States. Cell phone jammer can broadcast on any frequency and are effective against AMPS, CDMA, TDMA, GSM, PCS, DCS, iDEN and Nextel systems.
Jamming devices overpower the cell phone by transmitting a signal on the same frequency and at a high enough power that the two signals collide and cancel each other out. Cell phones are designed to add power if they experience low-level interference, so the jammer must recognize and match the power increase from the phone.
Corporations use jammers to stop corporate espionage by blocking voice transmissions and photo transmissions from camera phones. There are rumors that hotel chains install jammers to block guests’ cell-phone usage and force them to use in-room phones at high rates.