Figure 8-25. - Various components of a residential security/fire-alarm system.

Figure 8-26. - Floor-mat detector.

Since electrical resistance is measured across two wires (center and sheath), the sensor has the ability to detect a high temperature on a short wire as well as a lower temperature on a longer one.

The elements are mounted by clamps spaced along their lengths and the detectors, being all solid state, have only two electrical failure modes: open circuit and short circuit. Both of these conditions can be caused only by mechanical means and are minimized by rigid mounting. Figure 8-33 shows the construction and mounting details.

Figure 8-27. - Ultrasonic motion detector.

Ultraviolet-Radiation Fire Detectors Ultraviolet-radiation fire detectors combine large- scale integration circuit techniques with an ultraviolet detection assembly to form a simple, yet flexible, fire- detection system.