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[jediagh]

First special thanks to James S.'s post here: http://forums.x10.com/index.php?topic=13542.0
He tested this back in 2006 on the DS7000 (the model before the SC1200 from x10).
I did it today but wanted to share pics and video on how it's done to help guide those that need more than just text to "see" it in action.

WHAT YOU WILL NEED
1) First Alert Photoelectric Sensor Smoke Alarms with Escape Light (Model: SA720CN)
2) Radio Shack 5vdc/1A SPDT Micro Relay (Model: 275-240)
3) x10 DS10A Window/Door Sensor

TOOLS YOU WILL NEED
1) Soldering Iron
2) Solder
3) Flat head screwdriver
4) Voltage meter
5) small gauge wire
6) Needle nose pillars

Note the images are very big so I am not "embedding" in the message as the text will not flow right.
This is what the unmodified smoke detector looks like.
http://www.majhost.com/gallery/jediagh/tech/x10_smoke_0001.jpg

Turn the unit over and you will notice 3 small clips that hold the upper shell to the bottom shell.
http://www.majhost.com/gallery/jediagh/tech/x10_smoke_0002.jpg
Here is another view of how the clips "lock" into the upper shell.
http://www.majhost.com/gallery/jediagh/tech/x10_smoke_0005.jpg

Use a flathead screwdrive and slowly pull back the clips to pop them out.
When done you will be able to remove the top shell and see this

The bottom shell
http://www.majhost.com/gallery/jediagh/tech/x10_smoke_0003.jpg
The top shell
http://www.majhost.com/gallery/jediagh/tech/x10_smoke_0004.jpg

Now we need to remove the circuit board from the bottom shell. It is held in place by 2 clips.
http://www.majhost.com/gallery/jediagh/tech/x10_smoke_0006.jpg
http://www.majhost.com/gallery/jediagh/tech/x10_smoke_0007.jpg

So again use the flathead screwdrive and push the clips back to pop-up the board.
It will look like this
http://www.majhost.com/gallery/jediagh/tech/x10_smoke_0008.jpg

Now you can either pull the board towards you or use some needle nose pillars and remove those metal battery connectors first.

This is what it looks like when you pull the board towards you
http://www.majhost.com/gallery/jediagh/tech/x10_smoke_0010.jpg

Here is how it would look like with the battery leads removed.
http://www.majhost.com/gallery/jediagh/tech/x10_smoke_0018.jpg

Here is the back of the board.  A sea of soldering bubbles!
http://www.majhost.com/gallery/jediagh/tech/x10_smoke_0011.jpg


We are NOT going to mess with this side BTW.
Note that the flathead is pointing to where the battery connects for ref.

Here is the "magic box" the radio shack relay!
http://www.majhost.com/gallery/jediagh/tech/x10_smoke_0012.jpg

Now I'm not sure if it makes a difference how you connect the wires from the light to the relay.  I took out my voltage meter and tested to see which one was positive/negative on the light.  When holding how the TEST button and forcing the smoke detector to beep and light up the voltage meter either read +5 or -5 depending on how I was holding the leads.  This picture shows that RED is the POSITIVE side making the voltage meter read +5.
http://www.majhost.com/gallery/jediagh/tech/x10_smoke_0014.jpg

Based on the relay image I don't think it matters since as long as current passed into the relay it will cause the upper switch (inside the relay) to switch.

Here is the first 2 soldering points you have to make.
http://www.majhost.com/gallery/jediagh/tech/x10_smoke_0016.jpg
Again it does not matter which wire from the DS10A you connect to the 2 points on the relay.
WHAT DOES MATTER IS WHERE YOU CONNECT THEM. MAKE SURE YOU CONNECT THEM AS SHOWN

Here is the finished job of soldering the wires to the light.
http://www.majhost.com/gallery/jediagh/tech/x10_smoke_0017.jpg

Note that you will end up with 1 relay PIN not being used & that is OKAY!

--SIDE NOTE--
The relay is just a switch with the following PINS

1   2

3   4      5


When "off" the switch is connect between PIN 1 and 5.
When "on" the switch is connect between PIN 2 and 5.

To turn "on"/"off" you pass a current between PINS 3 and 4.

So when you smoke detectors turns on and it turns the light on.  We want that current to pass thru PINS 3 and 4.  This in turn will force the switch to move from PIN 1 to PIN 2.  When this occurs the closed loop that the DS10A had will no longer be valid.  It will be opened which is the same as when you "open a door" using the magnets.  So the DS10A will register an "open contact" and trigger the alarm signal.

---BACK TO INSTRUCTIONS--
Now put the circuit board back into the bottom shell, put the battery leads back in if you took them out and the relay as well.  Depending on how long your wires are you may have to play around to them them all in.  I used some rather long wires (green = 5"; yellow = 4")  I think 3" would have been okay but I wanted make sure I had enough wire.
http://www.majhost.com/gallery/jediagh/tech/x10_smoke_0019.jpg

Now when you go to put the upper shell on the relay is going to be in the way of this plastic part.
http://www.majhost.com/gallery/jediagh/tech/x10_smoke_0020.jpg

Use your pillars again and just tear it off.
http://www.majhost.com/gallery/jediagh/tech/x10_smoke_0021.jpg

Here is the finished product next to a standard First Alert detector.
http://www.majhost.com/gallery/jediagh/tech/x10_smoke_0023.jpg


Here is a video showing how when you test the smoke detector & it's light goes on the red light on the DS10A goes off as well (ie. sending it's signal to trigger the alarm).
http://www.youtube.com/user/aampr0ducti0ns#p/a/u/1/uwebGtMg5P8

I turned off the lights in the room in order to do the video so you can see the RED light.

Here is the final product with the SC1200. Note you will hear the chime of the SC1200.
http://www.youtube.com/user/aampr0ducti0ns#p/a/u/0/Sekin5n9tJ4

NOTE I WOULD RECOMMEND THAT IF YOU DO THIS TO NOT USE THIS SMOKE DETECTOR AS YOUR ONLY DETECTOR.  INSTEAD PUT THIS MODIFIED ONE RIGHT NEXT TO YOUR REAL ONE.  BY DOING THIS YOU ARE MODIFYING THE FIRST ALERT DETECTOR AND IF YOU EXPERIENCE A FIRE AND THE FIRST ALERT DOES NOT WORK IT COULD BE SAID IN COURT/INSURANCE PURPOSES THAT YOU DAMAGED A WORKING PRODUCT AND THUS IT DID NOT WORK.  SO INSTEAD USE THIS IN ADDITION TO YOUR UNMODIFIED DETECTOR ONLY

[Knightrider]

here comes the flood of +1's.  Glad I got the first one in.

 

[hawk1]

I'm second!!!   

[jediagh]

Almost forget total cost is about $20.

First Alert w/ light @ Mejiers = $10.88
Radio Shack relay = $4.69
DS10A = $3.75 (via ebay buyer who sells them in 3-pack for 11.27 free shipping)

Also this first one took me about 4 hours to do.  The next ones should be less time.
I have 8 fire detectors in the house in total.  I'm thinking I really only need 3 of these MOD detectors one per each floor hooked into the SC1200 that I have right now.

In the ideal world I would like to get another SC1200 and hook up 8 MOD detectors so that the recording that goes out said FIRE, FIRE, FIRE.  

Right now the sole MOD dectors is connected to my security system and I'm not sure if I will be able to "hear" it if I hear over the mic when the system is triggered.  I have 4 power horns as well so suspect that they may drown the fire alarm out.  Not sure will have to test.  The plan of action I am thinking is to hang up and call the SC1200 and get the status of the unit which in turn will tell me which sensor triggered it and if it is the fire alarm one then I know it's a fire.

Still working on the logistics in my head.  Need to save up some more $$$ to get another SC1200 really. =)
For now another $40 will do to get the house somewhat fire detected via the security system.

[HA Dave]

I'm second!!! 

Third.

[Brian H]

Also added a +1

If someone wanted to use a DS12A. They could wire the added relay in the smoke detector, to the extrenal zone terminal block in it.

[dave w]

# 5!!
Nice pix also.

[-Bill- (of wgjohns.com)]

#6!

 
 

[JMac]

Thanks - when I move up to the 1200 I'll follow your lead.  Great work!

[aptalca]

WHAT YOU WILL NEED
1) First Alert Photoelectric Sensor Smoke Alarms with Escape Light (Model: SA720CN)

Hi Thanks a lot for the detailed guide. I just ordered the smoke detector off of amazon to do the same mod as I just got the sc1200 a couple of weeks ago.

However, judging by the pictures, I think you have the model number SA304CN (http://www.amazon.com/dp/B000BDB708). That is the ionizing version of the SA720CN. I noticed that when I received my SA720CN yesterday and it looks a little different (http://www.amazon.com/dp/B000PFNCHI). I thought it would be fine since they should be very similar inside.

But to my surprise there was one difference that kind of ruined my plan. The led light on mine does not have the two wires on the sides exposed. The black plastic covers the entire circumference, hiding the wires. I have no idea how that piece is held in place. It does rotate about 20 degrees each direction, but I don't want to break the LED. My only option is to solder the wires to the backside as I can see the LED wires sticking out on the bottom.

Wish me luck, I'll let you guys know how it goes.


***EDIT/UPDATE***

I soldered the wires to the bottom side connections of the LED and it works like a charm. Thanks for the guide and most of all, the idea.

If someone wanted to use a DS12A. They could wire the added relay in the smoke detector, to the extrenal zone terminal block in it.

That is exactly what I did. I love the fact that DS12A's internal and external terminals can be set up as separate sensors on the sc1200.

All the DS12A's I have on the windows also have the simple GE 5150 glass break sensors attached to the external terminals and sc1200 sees them as different sensors. That way I can set up macros through AHP to alert me via e-mail if a window is broken as opposed to window or door opened whether the alarm is armed or not.

[Tuicemen]

 
As a thought you could trigger AHP to play a looping wav file when that sensor was tripped. 
The bigest issue would be hearing your PCs sound.
 

[dbemowsk]

This is a great writeup with very nice pics.  The only thing I can possibly see as an issue would be that since this looks like you put the relay in parallel with the LED, the amount of current draw from the relay and the LED together may overload the rest of the circuit.  Maybe not right away, but over time.  I personally would have come off the LED with a small transistor that used power straight from the battery, and used that to drive the relay.  I may be off base on this as I don't know exactly how much current the  device supplies to the LED.  Maybe Jeff V., Dave H. or one of the other electronics techs could chime in on this issue.

Great writeup never the less.

[dave w]

I may be off base on this as I don't know exactly how much current the  device supplies to the LED. 

There will be a current limiting resistor for the LED which will protect the transister or chip that outputs to the LED. Appearently there is enough current through the resistor to still light the LED and actuate the relay. If the extra relay load would cause a problem, it will be at that resistor.

[Brian H]

Unless it used one of those fancy LEDs with the current limiter inside it.
I used 5, 12 and 24 volt ones in the past.

[jlecount]

Very cool!

Looks like some of the photos are no longer up -- would you mind checking that out?  I'd love to try this!

Thanks for your effort here...
Jason