My Google searches are turning up no solution for this, so figured I would try here to see if anyone has tackled this topic yet. I’m looking for a plug-in (to save battery life) zwave or zigbee sound level sensor that can detect when the wall-mounted siren for my old home alarm goes off, and then the sound sensor would alert me through SmartThings. If I can set this up and get it working, then it will allow me to leave my old expensive alarm in place without monitoring, yet still be alerted through my SmartThings setup if the siren goes off. Any ideas for a sensor to fit this need?
why not figure out what voltage the siren runs off of, attach a relay to that, then run that into a contact sensor.
While maybe more work for you it will be less expensive than building a HA capable sound level meter.
I too have been searching for an inexpensive zigbee/zwave spl meter, alas no such device exists.
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Every once in a while one of these Ubi pops up on Ebay as cheap as $20. It has a SPL meter built in and works with Smart Things. You can make a lesson to trigger a switch at a desired SPL.
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Hi Mike. Thanks for the response. I’m not a particularly handy guy when it comes to building electronic solutions (although I do well with other stuff). The wall siren is a standard ADT siren that I got around 2001. It has a single thin round wire running from it to the ADT control panel in our closet and that’s powered by an AC adapter plugged into the wall, and the control panel also has a battery backup. Does this information help to determine what voltage the siren is?
You could treat it like a doorbell, in which case just putting a vibration sensor right next to the alarm might be enough. No wiring required. Some people have done that with doorbells. you’d just have to test it to see how many false alarms you got. 
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That’s an interesting thought JDRoberts. I have a SmartThings multi-purpose sensor that I can try that out with. I can stick it directly to the ADT siren box and see if it picks up the vibration when it goes off. Will post my results here as soon as I get home and try it out.
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Never mind this idea. Everything in that area vibrates that alarm siren box (front door slamming, closet door opening, etc).
@Mike_Maxwell can you provide any further details on your idea of a relay and contact sensor?
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What’s the exact model, or can you post a pic of it, then maybe we can find manual and see what contacts it has
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I know it’s not cheap, but the Netatmo Welcome camera detects Alarms / Sirens sounds and sends an Alert to your phone.
I was surprised last week when my Smoke Alarm in the Kitchen went off (cooking, not real smoke) and I got an Alert on my phone.
There is IFTTT integration and I use it for Motion, but sadly there is no Trigger for the Alarm yet 
@RudiP, the model number is ‘RX-7 Sounder’ and it says 12 volts DC and 150ma on the back of it. There seems to be a lot of info on Google for this unit.
The question here is whether they operate The same way as the other acoustical listeners, the kidde remotelync and the Leeo. In the US, there is a specific acoustical pattern assigned to smoke detectors and a different one for carbon monoxide detectors. Any smoke alarm sold as such must use that specific pattern. So, it’s fairly easy to create a device that will listen for that pattern.
Most of the security systems that I know do not use the smoke alarm pattern for the regular intruder alert alarm. They probably can’t, legally. Which means devices like the remotelync and the Leeo will ignore them.
The Netatmo welcome says it detects security alarms, but it may not do so with the same accuracy as a smoke alarm.
So is this ADT alarm the same as your smoke alarm? Or does it have a different acoustic pattern?
If it does use a different pattern make sure you get the netatmo welcome from someplace with a good return policy in case it can’t recognize the ADT alarm. But it would be very cool if it works. 
@JDRoberts, the ADT siren that goes off is the same for anything to do with the windows, doors, or smoke alarms.
Home depot had a zwave alarm detector in their smoke detector section last time I looked. I though about getting it, but the box says it only works with single alarm devices… I guess.it detects a continuous alarm and not the different beep patterns for CO or Smoke.
why not connect your whole system to smartthings? sounds like you have a honeywell ademco?
Is it the typical smoke alarm beeping? Or more of a siren? In the US, 3 long beeps is fire, 4 short beeps is CO2, but I think that only applies to individual detector devices, not a security system like ADT.
The acoustic detectors that listen for the beep patterns are very reliable. The ones that just go by decibel levels for siren detection tend to have more false alerts.
Not yet integrated to ST yet but will give you what you want -
http://www.amazon.com/Leeo-Smart-Alert-iOS-Android/dp/B00XMX4GUC/ref=pd_rhf_se_s_cp_6?ie=UTF8&dpID=31MOxl2T2UL&dpSrc=sims&preST=SL500_SR135%2C135&refRID=19Z3DM1SK7JK2VJ18FPJ
or this
you should be able to have a relay activate using the power from the siren. If that relay is wired to a microswitch it will in effect be exactly the same as turning a light switch on and off except the siren is doing it for you. I believe the AEON micro controller is supported by ST, I just got one that is going in this weekend. it sounds more complicated than it is 
no need to be scared of wiring it, I can walk you through it. The micro controller is made to go in an electrical box and add smarts, it watches if you turn a normal switch on and off & reacts accordingly.
wall plug —> micro controller <---- relay <---- siren
To build get an outdoor electrical box ($10), extension cord to power the micro controller [cut the end off and wire to microcontroller] ($10), a micro controller ($35), relay ($5), wire nuts ($5) and some black and red wire ($5).
should be around $70.
can you post a picture of the siren and possibly where it connects to the panel? does it look like this? if so the siren is being powered by 12V DC
http://www.ebay.com/itm/ADT-875936-RX7-INDOOR-SOUNDER-85-dB-A-10-FT-/150821660451
parts:
relay:
@pascal, thanks for your feedback. I’ll take a photo this weekend and post it. I’m totally unfamiliar with electrical wiring so I would need to be stepped through this almost like a baby. It’s the one area that I never did anything with when I was general contracting the construction of my house.
Isriam, this ADT system is from back in 2001…I have no idea if it’s even remotely compatible with SmartThings.
@JDRoberts, it’s an alarm system siren, nothing like a smoke alarm.
@anydaynow open the door to your security panel and look at the sticker on the inside of the door and post back the make and model number. If you had ADT you likely have a Vista or DSC panel in which case there are several threads on this community on different ways to integrate it with ST. You will be able to leverage all your alarm sensors with ST from door and window contacts to motions.
Here is one example of many:
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wow, thats an impressive project - quick skim on the instructions it looks like the alarm panel has a serial interface which folks figured out how to talk on. very neat