The first issues addressed pertain to technological terminology. The difference between "analog" and "digital" signals is explained, and "encryption" is defined as the science of writing secret codes to protect the security of communications. The article then explains wireless technologies, which have facilitated the mobility, flexibility, and covertness of visual and audio surveillance. Secure Internet-based camera surveillance has also emerged. In one instance of such surveillance, the San Diego Police Department gained the cooperation of a private company in using the company's existing Web-based camera placements to observe "flash-point" beach sites for criminal activity on a July 4th weekend. Another type of video surveillance described is that which typically uses cameras mounted on a helicopter or fixed-wing aircraft. In most cases these are licensed by the FCC and operate between 2200 and 2500 MHz. Also discussed is recent FCC allocation of a new band for fixed and mobile wireless services and the designation of the band for use in support of public safety. Among the concealed surveillance devices discussed are small digital video cameras that can be used to record criminal activity and transmit the video through a wireless connection. Various technologies of audio surveillance are also described.