A tether is a cord, fixture, or signal that anchors something movable to a reference point which may be fixed or moving. There are a number of applications for tethers: balloons, kites, tethered wind-energy conversion systems, anchors, tethered water-flow energy conversion systems, towing, animal constraint, and power-kiting. Tethers may break by various means; if a tether is a signal, then interruption by signal barriers breaks the tether. If the tether is a cord or rope, then upon reaching the breaking strength of the tether, the tether fails in its function. Failure modes for tethers are considered when designing arrangements where a tether is needed. When a tether or line breaks suddenly, backlash of the segments may cause severe damage or loss of life; safety links are sometimes used to prevent excessive tension in a tether involved in towing objects or persons, like in the towing of sailplanes; the safety link in a tether is thus a tether itself. Tethering objects to prevent theft of an object like a computer at a school or library is now commonly seen.