Ultrasonic sensor:
is a type of alarm which works on the principle of high frequency sonic emission to detect movement in a zone.

Ultraviolet:
is electromagnetic radiation with a wavelength of less than 400 nm and is not visible to the human eye.

Unbalanced cable:
is a type of cable in which the ends of the shields are grounded to different equipment with possibly varying ground potential. This unbalanced set up can give rise to ground loop currents and EMI induction.

UPS Uninterruptable Power Supply:
stores electricity and supplies power to a CCTV system during a power failure.

Usable video:
is the minimum video signal specified in the camera data sheet to generate an acceptable picture on the monitor. It is usually measured as a percentage of the full video.

Example: 30% usable video = 30% of 0.7 volts (full video or maximum video amplitude) = 0.2 volts