Surveillance is the monitoring of the behavior, activities, or other changing information, usually of people and often in a surreptitious manner.
Surveillance most usually refers to observation of individuals or groups by government organizations, but disease surveillance, for example, is monitoring the progress of a disease in a community

Outdoor Wi-Fi 11a.b.g Jammer device camouflage looks like the panel antenna or WiFi outdoor device. Wifi 11a.b.g jammers transmits power radio signals to cut off communications between PC or cellular phone and base stations without interfering with any communication.   Features and Specifications Tx Frequency: 2.4~2.5GHz, 5.1~5.9GHz Cover interface standards: 802.11 a/b/g Total output power:EIRP [...]

Mobile Bug Detector This handy, pocket-size mobile transmission detector can sense the presence of an activated mobile phone from a distance of one and a half meters. So it can be used to prevent use of mobile phones in examination halls, confidential rooms, etc. It is also useful for detecting the use of mobile phone [...]

Currently jammers & cellphones are banned in-flight operations.  Soon they would be buzzing with ringtones.  Recently the communications authority has proposed to allow passengers use mobiles on planes.

According to  FCC aCT, 1934  ”IT prohibits any person from willfully or maliciously interfering with the radio communications of any station licensed or authorized under the Act or operated by the US government.”  First time offenders may face either fines of up to $11,000 or a year in prison for each violation.

Cell phone jammer blocks transmission/reception of signal by creating interference at the same frequency ranges that cell phones use.   After which a cell phone  will lose the signal or signal quality will deteriorate. Sale of cell phone jammers is legally prohibited in US.

Jammers are illegal in England, the United States and most of the European Union. But the most basic jammer costs as little as fifty dollars in Hong Kong. By sending out a blizzard of radio waves, this cigarette packet-sized gadget will knock out a mobile phone signal within a radius of five to ten yards. [...]

The F.C.C. regulates the airwaves in the U.S.A. Here is their official line on jamming: The operation of transmitters designed to jam or block wireless communications is a violation of the Communications Act of 1934, as amended (“Act”). See 47 U.S.C. Sections 301, 302a, 333. The Act prohibits any person from willfully or maliciously interfering [...]