Failure modes of sensors


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Old 07-04-08, 09:57 PM
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Failure modes of sensors

Hey guys.

I'm not exactly excited about the prospect of false alarms. I'm planning on getting a Simon XT in the not-so distant future (but also not very soon either).

I read somewhere that 2% of burglaries occur through 2nd story windows. So I'm trying to piece together a system that will protect me against this. Granted my situation it is probably even "safer" - because I live in a not so great area.... It is unlikely a professional thief would target my neighborhood.

So anyway - I'm concerned both about false alarms and also having a reliable system...

I guess I'm just interested in thoughts as to where it becomes counter-productive to add more sensors in a second floor environment... Meaning, where the added complexity starts creating more usability problems than solving the reasonably slim chance of someone trying to break in through a second floor window.

Since I am more concerned about personal protection versus property protection, I'd like to minimize motion detectors. So to me that means transmitters on each window, and glass break sensors in each room. (Unless I find a way to add additional locking mechanisms to my vinyl windows to further guarantee them from being forced open - then I could just use glass break sensors in each room)

Sorry for rambling. I guess I'm just asking for overall thoughts ont he subject.
 
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Old 07-05-08, 08:52 AM
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If you have the money and the time to add sensors to your second story windows AND you feel it is important to contact them then I think you should do it. I have my second story windows contacted, but I do so to monitor if my kids open the windows ( I have windows that go almost to the floor and I fear a child could fall out if opened).
 
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Old 07-05-08, 09:29 AM
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Thanks kcxj.

One of the things going through my mind though - is aside from the investment in money... Is with the additional switches and glass break sensors - how much increased risk is there of false alarms?

I guess what I'm asking is how reliable are these wireless devices? Specifically the GE equipment.

Oh and if someone could explain what SAW versus crystal means... Well, I'd sure like to know.
 
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Old 07-05-08, 05:05 PM
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Unless your home has an unusual amount of RF "noise", the GE design transmitters are very reliable. They've been using the same basic design for nearly 20 years, so it's well tested. The typical battery life is about 5 years.

Go for it. Just shop your sources by price, as wireless transmitters can add up, cash wise...
 
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Old 07-05-08, 05:15 PM
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Originally Posted by Jack_Bauer
Thanks kcxj.

One of the things going through my mind though - is aside from the investment in money... Is with the additional switches and glass break sensors - how much increased risk is there of false alarms?

I guess what I'm asking is how reliable are these wireless devices? Specifically the GE equipment.

Oh and if someone could explain what SAW versus crystal means... Well, I'd sure like to know.
Jack,
PM me...I'll send you info on SAW vs Crystal that will make your head spin. Short story... SAW (surface acoustic wave) = good transmission range, good battery life, moderate cost...Crystal= Best transmission range, best battery performance, will cost you a few bucks more.
 
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Old 07-05-08, 10:16 PM
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Thanks guys.

I'm satisfied to know that crystal is better, and while more expensive - I'm not too worried about that.

I'm struggling a little with the overall design of my system... One that covers almost any possible means of entry, without compromising my ability to wander around at night if I can't sleep or want to check something out.

My living room (second floor) is just set back from the front porch below... And there's a door to my own front balcony on one half, and the roof over the front porch below on the other half. A total of four windows and one door. Granted I'm on the second floor - but houses on either side of me also have a balcony - and it would be pretty easy for someone to walk crawl across a board to gain access. (not likely but possible)

Anyway - I'm just strugglign to determine the most efficient way of protecting those 4 windows and door against any type of entry. I'd like to do it in a way that would allow me to use that living room late at night without turning off elements of the alarm. I may use a PIR and just aim it so it's FOV catches only the front 1/4 of that room, where all the windows are. Or of course, window switches and a glass break sensor.

Oh well - I just have a lot to think about. I tend to do things very thoroughly.

One final question - with respect to mounting switches on windows... Can't an intruder simply force the upper window of a double hung window down, leaving the lower sash in place, and not interrupting the circuit?

Thanks for reading all that
 
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Old 07-06-08, 10:19 AM
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If you have door and window contacts and glass break detection, the PIR is really only needful for instances with "away" arming. Most of the standard settings will do an autobypass for the PIR.

Motions are a "second line" device, if your perimeter is covered, limiting your own movement in the interior is kinda silly. If you have a keypad in your sleeping area, or a remote keyfob, you always have the option of switching from stay to away arming before you turn in for the night.

While the Simon XT is a capable all in one system, I'm really thinking that you are seeking capacity and capability that is a bit beyond one of these systems.
 
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Old 07-06-08, 12:09 PM
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with the overall design of my system

Yours is a classic Game Theory problem [it's your strategy against the burglars' strategy]

The local "crime analysts", paid by the state taxpayer dollars, may be able to help with that, if you can get their e-mail addresses.

Hopefully you can weed out some unlikely scenarios ["cut branches off the decision tree"].

I did hear if you can delay a burglar one minute, he'll go to the next house.

The alarm system may have the effect of raising the burglar's "level of perceived risk", and he may then also go to the next house. He no dummy!

Talk to the cops; they have the raw break-in data and the experience.
 
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Old 07-06-08, 12:18 PM
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Originally Posted by MrRonFL
If you have door and window contacts and glass break detection, the PIR is really only needful for instances with "away" arming. Most of the standard settings will do an autobypass for the PIR.

Motions are a "second line" device, if your perimeter is covered, limiting your own movement in the interior is kinda silly. If you have a keypad in your sleeping area, or a remote keyfob, you always have the option of switching from stay to away arming before you turn in for the night.

While the Simon XT is a capable all in one system, I'm really thinking that you are seeking capacity and capability that is a bit beyond one of these systems.
Thank you Mr. Ron - I much appreciate your input.

I apologize if I seem a bit all over the place here... Just that while most people are satisfied to hook up switches to their 2-3 doors and be done with it, I'm rather thorough.

I have six rooms and I was looking to avoid putting glass break sensors in each room as I kind of saw glass break sensors as having less reliability than PIR. (To me there's just a lot of variables that go into it working - yet not having false alarms. Although in general false alarms likely would only be a problem when I'm at home making noise and I'd be able to disarm the system prior to the alarm going off)

I have probably a few months to put together my system at this point... I'd consider a higher end "component" system, but I'm really looking to do multiple keypads - probably four, wirelessly. The XT support that. And it has some other nice features. I intend to operate the XT in silent mode though, so I am taking a fair amount of the benefits of the AIO system away...

Right now I'm thinking of using the NX650 switches, one in each room, in transmitter mode only - to hook up to wired sensors on each window (NC). That should save me a little bit of money - but more importantly reduce failure opportunities. (it would also allow me to put two switches on critical entry points for increased security)

Although I'd still like to understand how to protect against someone lowering the upper half of a double hung window?

Again my thanks for reading. My design process for something like this is a bit iterative, but in the end by doing research over a period of time, I'm sure I'll end up with something I am satisfied with. Especially with guidance from such competent people as yourself.
 
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Old 07-06-08, 06:43 PM
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Double hung windows are fairly simple: You put a set of contacts on both the upper and lower moving sections. You wire each pairs back to the hardwire input on your wireless transmitter as a NC series circuit. The details of where to place the contacts and what specific type to use will vary by the window and window frame construction.

For glass break devices, they are of best use for large panes of glass that someone could break and easily step in. (Sliding glass doors, picture windows, etc. In general unless you have an ususual house design, they are best applied on the first floor, it's a rare circumstance where breaking a window on an upper story is going to be an entry point.

Be careful trying to tie too many hardwire contacts to a wireless transmitter. In general, they recommend keeping overall external wire length under 10 feet. Remember, these things have limited power, and wire adds resistance. If the windows are fairly close together, it's no big deal, but you will likely run into trouble if you try to do a whole room of windows with one transmitter.
 
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Old 07-08-08, 06:16 PM
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Originally Posted by MrRonFL
Double hung windows are fairly simple: You put a set of contacts on both the upper and lower moving sections. You wire each pairs back to the hardwire input on your wireless transmitter as a NC series circuit. The details of where to place the contacts and what specific type to use will vary by the window and window frame construction.
Thank you MrRon.

So it is normal for people not to use the internal reed switches on these transmitters, and to use it purely to hook up to external magnetics?

It's interesting - I could really only find one (Ademco) form-c device out there. E.g, there don't seem to be a lot of NC based contacts out there?

While I'm quite comfortable doing this... I still would be interested to see pictures of how people wire these. I couldn't seem to find a website that showed a good set of two contacts mounted on a double hung window...

Originally Posted by MrRonFL
For glass break devices, they are of best use for large panes of glass that someone could break and easily step in. (Sliding glass doors, picture windows, etc. In general unless you have an ususual house design, they are best applied on the first floor, it's a rare circumstance where breaking a window on an upper story is going to be an entry point.
Yeah - I imagine it would be kind of difficult to get up on an extension ladder, bust the double pane windows I have, clear out all the glass, so someone can go head first through it.

I'll probably put a glass break sensor in my rear room that has a sliding glass door, and a glass door leading downstairs to my backyard. And maybe one in the front where there is a roof for someone to jump on and get easy access.

Originally Posted by MrRonFL
Be careful trying to tie too many hardwire contacts to a wireless transmitter. In general, they recommend keeping overall external wire length under 10 feet. Remember, these things have limited power, and wire adds resistance. If the windows are fairly close together, it's no big deal, but you will likely run into trouble if you try to do a whole room of windows with one transmitter.

Thank you for this warning. I wasn't thinking about that... Wow 10 feet doesn't give me a lot of options...

Thanks again...
 
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Old 07-08-08, 06:59 PM
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Normally closed contacts are the _standard_. Normally Open (and form C) contacts are special order items, for the most part.

The dual window contact wiring is very simple. Two conductors come from each contact. One leg of each is tied to each other. The remaining 2 wires are what gets connected to the input of the transmitter.

Electrically, it's a simple series circuit.
 
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Old 07-09-08, 07:04 PM
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Originally Posted by MrRonFL
Normally closed contacts are the _standard_. Normally Open (and form C) contacts are special order items, for the most part.

The dual window contact wiring is very simple. Two conductors come from each contact. One leg of each is tied to each other. The remaining 2 wires are what gets connected to the input of the transmitter.

Electrically, it's a simple series circuit.
Thank you MrRon.

I do understand the concept - I'm a controls engineer...

What I'm just a tad curious about is how to do a nice installation. I have vinyl double hung windows (double pane glass)... And I was just curious about the mounting of the sensors. For instance on the top window, I imagine I should put the sensor horizontally across the top of the window. (so as to not interfere with raising the lower window) There is a slight offset though as the window slides into a "lip". So the contacts would be off by maybe 3/32". Then I'd wire that in series with the lower contact, which would probably be spaced towards the top of the lower window... So I could open the lower window, with a second magnet mounted further down - so when the window opened up (for say mounting an AC unit), I would still have a "made" contact.

So I think I figured most of that wiring out - just I wouldn't have minded seeing how someone more experienced than me did it.

With respect to contact sense.... I think I got bit by the "shelf state" qualification of contact sense.

The Ademco contact product brochure says "Form A" which I interpreted as NO. But I assume now that it is "shelf state", without the magnet adjacent to it... And when the magnet is adjacent, that NO contact closes. (That's my understanding at least right now)

Thanks again
 
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Old 07-09-08, 08:11 PM
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Yes, the contacts are closed in the presence of the magnet.

As previously stated, the details for putting contacts on vary a good bit by the style and construction of the window. Vinyl windows are a notoriously difficult issue because they typically have a small reveal on the frames.

Try looking at the site of one of the larger makers of alarm contacts:

http://www.grisk.com/security_products.htm

or

http://www.tanealarm.com/magnetic_contacts_101.asp.

Some of them have a wide variety of contact sizes and configurations that might do the trick for you and look decent.
 
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Old 07-11-08, 03:19 PM
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Thank you MrRon...

I guess it all comes down to planning - to research the switches that fit my application before purchasing.

Why do some contacts come pre-wired with 12" (or so) wires?

I mean do installers typically want to deal with soldering wires together?

Also - and this might be my final question... Some switches come with self adhesive backing... Do people actually use that? I'd think that with sun shining down on windows, that perhaps the adhesive would fail... Gravity + heat + time = alarm going off?
 
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Old 07-11-08, 04:56 PM
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The ones with the leads are typically used for prewiring a building during construction. Very few installers solder the connections (heck, I'm one of the few I know that still keeps a solder pen in my truck), they use crimps like the B-connectors ("beanies") or scotch-locks to attach the leads to the field wiring.

Trust me, that 3-M double side tape they use on these things lasts for decades, especially applied on a clean surface. The only time it's an issue is with metal windows that tend to sweat in some climates, and even then the failures are very rare. The stuff actually gets harder and tougher with age.
 
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Old 07-12-08, 06:23 AM
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Originally Posted by MrRonFL
Trust me, that 3-M double side tape they use on these things lasts for decades, especially applied on a clean surface. The only time it's an issue is with metal windows that tend to sweat in some climates, and even then the failures are very rare. The stuff actually gets harder and tougher with age.
Wow.

So it's common for professional installers to just use the adhesive backed ones???

What do they surface clean with? Just water, or something like acetone?

How closely does the magnet have to be lined up? I'm thinking in the "depth" dimension, where the window slides into a "sleeve". I see up to a 1/4" mis-alignment. Would I have to use a spacer in there, or in general wouild a device witha 1" gap still work?
 
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Old 07-12-08, 11:42 AM
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FWIW, Most of the sensors in my casement window sensors are indeed put in with double-sided tape, and they were installed 19 years ago when the house was built. They're still stuck on pretty tight, I had to replace a couple of casements and pull the sensors off, they were well connected.
 
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Old 07-12-08, 07:37 PM
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Most people use basic rubbing alcohol to clean the surface. Acetone is actually a little too aggressive.

They make contacts with wider gap tolerances, and the rare earth magnets that give you more leeway. In general, the bar shaped contacts are more alignment tolerant than the pressfit style contacts. Again, you have to shop 'em to match the application. For the most part 1/2" is the typical gap tolerance. The smallest micro style tend to be more in the 1/4" range.
 
 

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