Hello every one, I know this topic may be duplicated or already discussed but I have not found any answer for this.
My question is because I want to be able to disarm my smartthings system even if I lose power/internet connection. All sensors an siren I have configured run locally but if I’m away and there is a power/internet lost I won’t be able even to enter to my house without having the siren sounding. I have installed the CoRE smartApp disarming the house when I open my smartlock but this runs on the cloud. I want to develop an SmartApp to disarm the house under this scenario, but I don’t know if there’s a way to develop this that runs locally or if someone in the community has a workaround to solve this. Some guys recommend to buy a zwave keyfob to arm/disarm the system locally, which sounds great, but I wan’t to be sure that there isn’t any other way before buying a keyfob.
Thank you so much for taking time to read this question.
Missael Maciel
no custom apps are allowed to run local. here is a list of devices that run local and you could possibly use to disarm SHM:
As @Automated_House mentioned, unfortunately at the present time no custom code of any kind can run locally.
https://support.smartthings.com/hc/en-us/articles/209979766-Local-processing
The only stuff which does run locally is the official smart lighting app and a tiny bit of smart home monitor, but, as you noted, you can’t arm or disarm it unless your smartthings cloud account is available. Even routines don’t run locally. So I don’t see how a key fob is going to help disarm with a SmartThings installation if all that’s available is local operation.
There are sometimes some workarounds that can be created depending on the exact situation that you are trying to deal with.
So you have to look at each use case individually.
If you arrive home, your system is armed, your local power is operating, your local Internet is down, and you have an alert setUp to trigger the siren if a specific sensor fires, then you could have a minimote that could turn off the siren. But because you can’t disarm smart home monitor, the problem is the siren might keep going off over and over as sensors continued to trigger . 
That’s why the very small details matter as to exactly which sensors would be active.
You could also have a minimote set up that would turn off a smart plug that your hub was plugged into. And you could do that even from outside the house. For most people, that would then stop any sirens from going off. But it would also mean none of your other smart lighting automations would work, either.
So again, you just have to get really specific about exactly what you want to have happen under exactly what conditions and then you can try to figure out a way to do it. But what you cannot do is change the armed status of smart home monitor without having access to your SmartThings cloud account. 
Thank you so much for your reply!
What you comment it is extremely disappointing! Your house security and monitoring 100% internet dependent is not too much security and reliability 
Some guys in the forum ensures that the default routines (I’m back, goodbye) run locally, customs routines are the ones running on cloud, that’s why the suggested the keyfob. If this isn’t true, a keyfob isn’t any justified device to buy, neither an arrival sensor.
Definitively ST platform is not reliable for security topics, it may work only for automations. I will give a chance to different HUB (like wink) but I have to do more research on this.
Thank you so much!
Missael Maciel
Routines don’t run locally.
Like many people, I use a completely different system for security. I use SmartThings for convenience notifications like getting a notification if the guestroom window was left open and rain is expected. SmartThings does that very well. But it just doesn’t meet my requirements for a security system. You can find much discussion of this in the forums. Different things work for different people. 
Completely agree with you! ST is not a fully functional solution for security, it has many gaps. Hopefully ST developers are working covering this gaps. With the HW platform that uses the HUB it is almost unjustified it has not the capability to run routines locally, the lack of local interface via IP for configuration and 100% cloud dependent. As you said, for automation or to monitor minor things it works great but this limitation is quite disappointing.