I need to find an easy, cheap-to-construct outside intrusion system
(several detectors/monitors outside that will set off some kind of an
alarm inside a motor home a hundred to a few hundred feet away). Unless
anyone here can offer a better suggestion, I'm looking for really
easy to use/understand schematics or plans so I can build the system
myself.

"Easy" to build, defined: During the war for the freedom of the
Republic of South Viet Nam, I was an electronic tech in the army, but
have forgotten most all that, and my only recent such experience was
building a VERY (!!) simple 12 vdc ultrasonic generator on a
breadboard.

"Cheap to construct" defined: I've been out of work for a year
while recovering from a black widow spider bite, my last job won't
take me back, and the only income I have is unemployment and $$ from
stuff that I inherited that I'm selling.

"The Idea," explained: Due to the above bite, I had to give up my
apartment, lived in a friends camper for a year, and then somebody just
recently "gave" me a 24-ft. motor home which I am currently trying
to make drivable and livable but for which I cannot afford to pay for a
space in an RV park.

So, I thought I might offer to park the RV on sites (construction,
church, whatever) and offer night security monitoring via the use of
intrusion detectors placed by me around whatever site the MH is on, the
thought being that they could set off an alarm in the MH that would
wake me up [ unless I can make a business out of this, I still need to
job hunt during the day ] and I could then take whatever steps would be
appropriate ... like shining a big ole' spot light in the direction
of the detector that was set off or, better yet, calling the police

Any ideas, suggestions, or links that might help would really be
appreciated.

Christopher A. Steele
San Diego, CA.