External Motion Det. vs. WIndow/Door Sensor

[mike]

Most home security solutions seem to focus on
door and window sensors to detect intruders.
Why is that?

My initial thinking is to focus on external
motion detectors.  WHat am I missing?  are
external M.D.s not reliable?

[iceblue]

Hi Mike,

External motion sensors are not practical in
that the environment is not controllable.
Kids with soccerballs, US mail carriers,
dogs, birds, sun and nature, are just some
of those uncontrollable factors.  You would
experience so many "false" (non-hostile)
alarms as to make your system ineffective
(i.e., boy who called wolf).  Using high-
mounted (inaccessible) cameras (either real
or quality dummies) can be a deterrent as
can signage and effective lighting.