Hello, the main question is, how did you turn off the internet? If you turn off the router, it won’t work.
Yes I unplug my Deco from the power but I think I found the issue why they do not sound both in the same time as one of my detectors is on bedroom witch is like 7m from the M3 hub with an wall between so once I cut off the internet my others hubs like M1S goes offline the zigbee mesh there can be broken and the M3 doesn’t see the second smoke detector and my be this is why it doesn’t send the signal to sound the alarm on that too.i will check tomorrow again as today if I cut again my WiFi my wife will cut my things 
off
Deco is a router, when you turn it off you break the entire Zigbee control chain. sensor->gateway->router<-gateway<-sensor
Yeah I got that now from what I know I need an smart plug in between M3 and the bedroom so that zigbee be stable enough so the M3 to can send that command for alarm to sound when internet is down.will check tomorrow if I bring both detectors on the living room and check them like that if they start to sound both in the same time when one of them detect smoke.with internet is easy as my M1S extend the zigbee connection to my bedroom and makes it strong once it goes off line the zigbee mesh on my bedroom is broken and I think M3 doesn’t reach that smoke detector anymore.well trying different aproveches is how we learn and can help others too
Ah, I see what you mean about the Zigbee mesh, but in my case, the physical distance or signal strength isn’t the problem.
To test this, I don’t turn off my Wi-Fi router. We have a DSL connection, so to simulate an internet outage, I simply pull the telephone/DSL cable out of the wall. This means my entire local network (Wi-Fi and LAN) stays fully active, and all hubs remain powered on.
We can actually prove that the local connection between the M3 and the M2 is working perfectly even without internet: when the alarm triggers offline, the built-in siren of the M2 does go off! This means the M3 successfully sends the alarm command over the local network to the M2.
The mystery is this: why does the M2 receive the local command to turn on its own built-in siren, but fails to pass that command along to the smoke detector paired to it?
I hope this clarifies the setup. It really seems to be a software or routing limitation within Aqara’s local link features rather than a signal drop.
Hello, thank you for the detailed explanation.
Please write to support@aqara.com.
You can also copy the link to your topic in the forum discussion into the email.
Yeah all this are still an mystery.i am talking with aqara support to see why if 2 smoke detectores in my case are paired to M3 doesn’t run the siren both when one detect smoke locally when internet is down.as of now what Aqara told me is what I post here regarding the grouping alarm devices to have them both enable.ether way tomorrow I will make more tests and see if I can manage to make them both sound without internet
Wow, wait a minute! I haven’t even tested that scenario yet—does that really not work either?
Aqara support previously told me that if smoke detectors are paired to different hubs, the linkage only works with an active internet connection. But now you’re telling me that even if you pair two smoke detectors to the exact same M3 hub, the second smoke detector stays silent when the internet is down? That sounds crazy and completely defeats the purpose of a local hub like the M3.
I was actually considering migrating all my smoke detectors to a single M3 hub and just using Aqara smart plugs as Zigbee repeaters across the floors. But if what you’re saying is true, that workaround wouldn’t fix the problem at all…
Please let me know what you find out during your tests tomorrow. I’m really curious to hear the results!
Sure tomorrow I will do more tests till I receive an answer from aqara support and once I have something I will post here
New update about the tests I made today
With internet On I ungroup the detectors then I pressed 3 times on M3 hub button to start binding devices then on each smoke detector one by one I pressed 3 times his button wait till the M3 says that device added and did the same thing for the second detector all were binding well then I turn On grouping devices on each detector and test them without internet.now the weird part is that now M3 siren sound too with the siren from one smoke detector but the second detector was still silent.now since I am out of ideas I must wait and see what aqara support will answer to my email.with internet all works well but when comes to using them locally without internet only M3 and one smoke detector sirens are working but the other it is still silent.
Today aqara support contact me and ask for devices id and more info and told me that they will investigate the issue on why smoking alarm doesn’t work properly having the group alarm devices enable and without internet of course.
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That’s a great coincidence! Aqara support actually contacted me today as well. They asked me to approve a “Request for device diagnostics access” directly inside the Aqara app. It seems like they are finally looking into this offline behavior for both of us. Let’s hope they find a solution or a bug in their firmware!
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@dinni @Nicolajsen
Se her
Yes as you never know what that day come and you need them to work with or without internet perfectly