Hi Eric,
If there is access from the basement below most of the time door
alarm sensors are easy to wire even on an older home. French
doors usually have one door that must be open before the other
will move. Some older models allow either door to operate
independently of the other. If yours are of the former type you
only need to put sensors (called "contacts") on the door that
moves first.
The simplest way to protect French doors is with a roller/plunger
type sensor installed in the frame on the hinge side. I've tried
numerous brands and found that most tend to jam shut after a few
years. The one exception, IME, is a model from Sentrol (now part
of GE Security) called a 3005. When installed properly about the
only thing that can present a problem for these is paint. Just
don't paint them. This is how I've done it a few thousand times.
Using a 3/4" speed bore, carefully drill a hole in the hinge side
of the door frame, 2" above the threshold and parallel to the
floor. Make the hole about 2" deep. STOP.
Swap the drill bit for a 1/2" diameter, 16" long bit (often
called a "feeler bit"). Place the tip of the small bit inside
the large hole. Raise the drill motor so that the bit is about
60º off the floor. Swing the motor outside the door about 3" so
that the small hole will appear in the basement. By drilling at
this compound angle you won't wind up going through a 10-12"
joist.
Mark the cable with a fine point, Sharpie laundry marker and
shove a few feet of it into the hole. I like to use 22-gauge,
4-conductor (22/4) solid cable for alarm sensors. The jacket is
just a little smaller than that 1/4" hole you just drilled and
the solid core stuff is easy to push through to the cellar below.
Have your SO pull enough cable out in the basement to make neat
turns over to where you will hang the control panel cabinet,
leaving a couple of feet extra at each end. Bend the extra pair
of wires out of the way but don't cut them off. They'll come in
handy if you accidentally cut or short another wire with a
staple.
Solder and tape or heat shrink the connections at the sensor end,
place a tiny dab of silicone sealant (RTV or bathtub caulk is OK)
on the flange of the sensor and shove it into the hole. There
are screw holes to mount the sensor but I prefer a dab of RTV.
Leave a 12-18" "service loop" of cable in the cellar below in
case you ever need to change the sensor.
Most US homes built in the 1920's are of "box sill" construction.
That means the wall is open from the bottom of each first floor
window to the top of the foundation. Joists rest directly on the
foundation or, in some cases, on top of a double layer of boards
called a sill plate which is laid flat atop the foundation. At
the ends of the joists a board is nailed in place to close the
outside. Short, horizontal boards called fire stops are placed
between the joists in the basement.
Very few houses from the 1920's have adequate insulation. Some
have had it blown in later. Some have nothing at all. No matter
which you have it's not hard to fish cables through the outside
walls.
Keypads, motion detectors and such usually use the same
4-conductor wire mentioned above. Make a small hole in the wall
where the device will be installed and shove a little cable
inside. If you meet no resistance at all it's probably
uninsulated. Shove enough cable in to reach the floor plus an
extra couple of feet.
In the basement, use a 3/4" speed bore (sometimes called a
"paddle bit" to drill a hole in the fire stop below the detector
or keypad location. Make the hole at about a 45º angle so it's
easy to feed an electrician's snake into the wall. I like to
mark the snake a foot or two longer than the height of the cable.
Push the snake up until the mark reaches the hole and slowly pull
it back, making a couple of turns with the handle as you go to
snag the cable. Once you have the cable the rest is easy.
Note: Some older US homes have diagonal hurricane braces
installed between the last two studs next to each corner. In
particular if the house is in New England and it was built in the
late 20's to early 30's avoid corner locations.
Also, some homes have horizontal fire stops midway up the walls.
This was not too common in the 1920's though it is fairly common
on more recent construction.
With a little patience and a modicum of tool skills, most people
can install a hard-wired security system in a weekend or two.
The advantages of hard-wired are threefold. It's not likely to
become obsolete in your lifetime. It requires less maintenance.
There aren't a lot of boxes on the walls (makes for a higher WAF
rating).
Installing four or five door sensors in a 1920 era home should
only take a few hours. The keypad and siren(s) shouldn't be a
major problem if you avoid putting them right next to a corner.
There are flush-mount, interior sirens that can be installed at
heater vent height, a few inches above the baseboard. They look
like air return grills only smaller.
If you want to place a keypad on the second floor, go to the
attic and look for the DWV stack. That's a black pipe sticking
up through the roof to vent the "poop pipe". In the 1920's no
one had large hole saws since they didn't yet exist. The DWV
stack was fed through a square hole cut in the top and bottom of
each level, leaving a handy void (no pun intended) where you can
run cables for an attic or outside siren, second floor keypad,
smoke detectors, etc.
Feeding down to a bedroom keypad from the attic is easy. Look
for a flat 2x4 board. That's the top of the wall. Wires
emerging from that board near the bedroom door are from the light
switch. Drill a 3/4" hole an inch or two to one side from the
110 VAC stuff with your paddle bit and drop the wire in the hole.
If you need more help planning or picking out a system, contact
me if you like. I sell this stuff to DIYers in an online store
in case you're interested.
--
Regards,
Robert L Bass
Bass Burglar Alarms
The Online DIY Store
http://www.BassBurglarAlarms.com
