# How is pre-wiring done for motion sensors / alarm system in new construction?

In new construction, how is pre-wiring done for alarm systems, when then alarm may not be installed right away (or ever)?

It makes sense to me to actually install recessed door contacts (they're only a few dollars each) and run the wiring back. I suppose if using window sensors it would make sense to do those as well (or just use motion sensors / glass break sensors and save a lot of work).

It also makes sense to run at least a couple wires up into the attic, for a siren or other future use.

What I'm not sure of is motion detectors. What's the best way to leave the wires to be able to hook them up later? Any tricks to avoid cutting a giant hole in the wall later?

Any other considerations to pre-wiring?

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Always assume you will forget/not know about something. So it will be easier to put in an extra conduit/ access hole during building(renovations) if you want to add more cables later. Put junction boxes in easy access places (eg loft udner a floor board, removable tiles, etc) Its easier to regrout a removal tile than re tile a whole section because your cat5 was supposed to be cat6e... Generally run conduit in the wall/plaster for running wires for future wiring- it can be bent to 90 degree turns and easily joint- it makes life so easy. –  ppumkin Nov 9 '11 at 10:10
Why not just fit a wireless alarm? (Then you just need a power wire to the panel and the sounder.) –  Walker Nov 9 '11 at 16:46
Wired alarms simply work better (no interference, no batteries to change), and are cheaper. The idea of pre-wiring is to avoid the only option being a wireless alarm. For example, a wireless door contact is ~$50 (and requires periodic battery replacement), and a wired one is <$5 (for sensor + cable). May still make sense to use SOME wireless sensors later, but it's not that difficult or expensive to pre-install recessed door contacts, and wires for motion sensors. I'm considering this as a DIY pre-wire -- the economics may change if you have your contractor or a pro alarm company do it. –  gregmac Nov 9 '11 at 18:06
Think about where you might want remote keypads with displays as well as sensors. Our house is mostly done with wireless sensors; wish we could have a keypad in the bedroom with a display. –  TomG Jan 15 at 2:10

When we do drywall, if there's a loose wire (e.g. electrical line for a hard-wired dishwasher), we cut a small hole and pull it through during installation. Pretty easy to do while everything is open and you can see both sides of the drywall. Leave plenty of slack so it can be fished through the drywall before it's been attached to the wall, and the hole can be made even smaller.

The other option is installing a J-box like you would for phone or cable wires, and leave an opening in the drywall like you would for any other J-box.

For other considerations, I'm a huge fan of conduit. No need to go to every door/window, but it wouldn't hurt to run some to where you want the main key pad, to the attic, and to your telecomm connections.

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Sorry, I meant to add in my question that the alarm may not be installed right away, so it would be better not to have wires sticking out of the wall. Adding an alarm in an existing house can be difficult, especially running wires on exterior walls, and for <\$100 of cabling it seems like a logical thing to do before drywall is up. –  gregmac Nov 8 '11 at 15:29
In that case, running the wires to a J-box and putting a blank plate on it would be easiest. But with alarms today, most are installed post-construction using wireless sensors, with a wired device being used only where it's convenient. –  BMitch Nov 8 '11 at 16:43

I pre-wired my house for an alarm since the alarm got fitted at the very end. I figured it would reduce the work required for the final install. I installed wires for the motion sensors, reed switches for under-house access, the control panel and the siren. From memory, some units require 6-core (such as the control panel) and some 4-core so I think I just ran 6-core everywhere.

Since I knew the alarm I was going to install and knew where the sensors and control panels would be, I ran the cables to those locations and just left them there to be plastered over.

For the motion sensors, I had roof access so it was easy to poke a hole though the ceiling at install time.

For the panels, I positioned these near light switches. At install time, it was easy enough to locate the cables (near the power lines) and pull them though the hole in the wall used for the control panel.

The reed switches were under the house so also easy to wire up.

The alarm unit also required a phone line and power. Part of my plan was the location where the unit would live so I ensured the sparky wired phone and power to the appropriate location.

I had an alarm guy install the actual unit. Having the wires pre-laid reduced costs, though he added a screamer to the system.

I did not bother with window or door sensors since I have a lot of windows/doors and the motion sensors will trip once the guy enters the house anyway.

BTW: I put coloured PVC tape on the wires at 2~3 metre intervals to make it easy to identify what cables went where.

BTW2: I have a (renovated) 1920s house with sizable cornices. In one location, the plasterers incorporated the senor cable into the cornice, allowing the sensor to be attached to the wall rather than hanging from the ceiling. This looked a lot nicer, I wish I had done it everywhere.

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We simply leave slack through a nm staple and bring the end to nail that is hammered into the corner of the stud. Dry wall guys do a good job at avoiding pinching the wire but if not just pull out the slack.

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