That’s a bit of a loaded question. The v1, v2, and v3 SmartThings hubs are dependent on the cloud for most things, so when your internet is down, or the SmartThings cloud is down, so is your security system. These weren’t really designed with security in mind, and are therefore lacking in several regards when compared to systems designed specifically for home security.
The ADT SmartThings hub was designed with home security in mind, so it has cellular back-up, can be armed or disarmed locally (not cloud dependent), has entry/exit delays, has an officially supported keypad, and comes with a touchscreen with a built in siren. One downside is that only ADT sensors can be used for the security monitoring with the ADT hub. They’re clunkier and quite a bit more expensive than many of the other sensors available.
If you are looking at getting into smartthings and you already have a home security system you should look at https://konnected.io/. I got in on the kickstarter for it and it has been amazing. It removes the logic board from your old “traditional” alarm system and adds your sensors and sirens to smart things.
The only full blown security system that smartthings is part of and manages without cloud interaction is the ADT Smartthigns Panel. All others will be cloud dependent and subject to cloud and internet access issues. The previous poster is mostly correct about the system except the sensors are not really any more pricey then any other Z-Wave/Zigbee Sensors. They are actually really reasonably priced in comparison. I have seen some z-wave door sensors in the 40-50$ range. The ADT Door sensors are $25 when not on sale, and have been as low as 10 at times.
With the ADT Panel you will also want to look at a Smartapp called ADT Tools 2. The smartapp will enable certain functions that are not present with the default Alarm integration. It will allow you to use the alarm to trigger actions with Lights, Sirens, and your Arlo cameras connected to smartthings based on alarm activity.
The system can be monitored if you want, but it doesn’t have to be. The monitoring cost for security options alone can be from $21 to $25.
The only real Smartthings limitation with the ADT Panel is the need to use ADT sensors for alarm activity if you want it monitored by ADT. All of the ADT Sensors integrate back into Smartthings and can be used for automations.
I have had the panel for almost 1 year, have 18 ADT sensor, 3 Water Leak Sensors and 1 ADT motion sensor. So far it all works well.
The only other negative thing i have hears is from someone that indicated they couldn’t get the wireless sensors to span their house. I guess the range wasn’t good enough. I have only heard that once though.