Motion detector wiring is usually included as part of the prewire for all hardwired home security systems. Passive infrared motion detectors, or PIR’s, are your best “second line of defense” after the magnetic door and window contacts.
If you’re considering a DIY home security system, you should consider wiring for a motion detector or two for protecting the interior of the house. If you have a home alarm company doing the wiring, they will likely include at least one PIR sensor in their standard prewire.
Motion detector wiring should always be home-run from each sensor back
to the alarm panel, without looping. This makes it easy to put each
detector on its own separate zone, and makes troubleshooting faster if
there’s a problem.
Sensors using passive infrared technology are most sensitive to movement across their field of view, and are very effective in small to medium sized rooms. Every motion detector comes with an installation sheet showing recommended mounting heights, coverage patterns, and adjustments. Amazingly enough, I recommend that you follow these instructions…!
If you have PIR sensors without any paperwork, here are some general wiring and mounting guidelines:
For most rooms, run wiring for each motion detector to a corner of the
desired room, at a height of 6-8 feet. Corner mounting will give the
best coverage of most square or rectangular rooms, without being an
In hallways, a PIR sensor will be slightly less sensitive. Movement
directly toward or away from the unit will not be picked up as quickly,
but will still be detected. Route motion wiring at 6-8 feet high, or
near the hallway ceiling if it’s lower than this.
Locate motion detectors so that they divide or break up the house into sections, rather than trying to cover every square foot. This usually means wiring a detector along each major traffic path. Hallways, entryways, kitchen areas, and family rooms are good locations. For most homes of 3,000 square feet or less, a detector in two or three areas will provide good coverage.
Run motion detector wiring to the corners of rooms for best coverage. A
passive IR detector is most sensitive to movement across its field of
view. Wiring for a corner-mounted motion detector gives you good
coverage of the area, and also helps the detector “disappear” into a
corner of the room for less visual clutter.
Install wiring for a motion detector in any area where you feel you need
extra security. Wiring for an additional detector is smart, and will
give you added protection for a master bedroom closet, gun or jewelry
safe, computer room, etc.
Dogs, cats, and many other animals may be a part of your family. This
means taking them into consideration when planing your home security
After years of helping people, pets, and alarm systems live together, I have some suggestions.
If your pets are free to roam the house while you’re away, you can
simply choose not to activate the motion detectors. This is done on most
systems by arming in “Stay”, “Home”, or “Interior Off” mode.
Confine pets to an area without motion sensors while you’re out. A laundry or utility room is often a good location, and a pet door can be installed if there’s an exterior door to the room.
Pet alley motion detector wiring lets animals move below the protected area, while still protecting against human intruders. See the pet alley section below.
Pet Immune motion detectors are designed not to trigger for animals under a certain weight limit, usually 50-100 pounds or so. This feature usually involves restrictions on the mounting location and height of the unit, sensitivity adjustments, etc.
In my experience, meeting the requirements for a pet immune detector is difficult in the average home. For instance, some manufacturers stipulate that you position the detector such that a pet cannot approach within 6 feet of the unit.
Since dogs and cats can trip most motion detectors, the best solution is to keep them in an area without motions when you leave the house. There are ways around this inconvenience, but one of the easiest is to use a pet alley.
This trick is often done with motion detectors in hallways. The idea is to invert a standard motion detector and mount it 3 to 4 feet above the floor. This creates a so-called “pet alley”, allowing average-sized dogs or cats to pass under the detection zone. Wiring for a pet alley means animals can roam the house freely while you’re away, and don’t have to be restricted to a laundry room or other non-motion protected area.
Visonic, a leader in motion detector technology, has taken this to the
next level with its Spy motion detector. The spy is a small cylindrical
sensor designed to work well in a pet alley application.
Wiring for Spy motion sensors should be done in hallways for the best
capture of motion, without risking false alarms due to your favorite
Be careful to use pet alleys mostly in hallways. They don’t work well in
regular room spaces, because pets climbing on furniture can still
trigger the motion sensor.
Most motion detectors are designed to be surface-mounted. Bring motion detector wires out of the wall framing onto a nail driven partially into a stud, and wrap the wire around the nail. After drywall is installed, the motion sensor can be attached to the stud or drywall with screws and plastic anchors.
Motion detectors use 22-gauge, 4-conductor wiring. As with all alarm system wiring, solid or stranded types are both acceptable.
Two wires, usually color-coded red and black are used for 12-volts DC
power from the main alarm panel. The other 2 wires, green and yellow (or
white) are used for the burglar alarm loop.