Use a different system? 
Everyone has different priorities and requirements for a home security system. Many of us in the community (myself included) use a completely different system for home security than SmartThings.
In my case, I have several minimum requirements for the home security system:
One) it be able to send notifications when either power or Internet are out
(SmartThings relies on The Internet to send notifications, even push notifications to your phone – – it has no cellular communication option )
- it communicate with a monitoring Center that can dispatch fire as well as police response
(the paid service that SmartThings integrates with, scout, can only dispatch police, not fire)
- it have a customizable entrance and entry delay for the security system
(Smart Home Monitor does not, and if you use custom code to introduce one, it again will not work unless the smartthings cloud is available since custom code cannot run locally)
- it provides a means for arming/disarming the system if the Internet is not available
(SmartThings does not)
- It allow me to postpone any system updates until the time of my choosing.
(Smartthings does not, even for updates which will take the system off-line temporarily)
- it has a maintenance free operating period of at least six months and preferably a year.
I have a security system which meets all of the above. It has worked well for about 10 years. The only thing I don’t like about it is that I feel I pay a little too much on a monthly basis. But having now gotten much more precise about my requirements and investigated many of the less expensive systems, I feel a little better about what I’m getting given that the cheaper alternatives, including SmartThings, don’t meet my minimum requirements.
Your own requirements may be very different, so each person has to judge for themselves. Just understand what it is that you’re getting.
SmartThings themselves in their usage guidelines say their system should not be used for anything which might affect safety or security, including protection of valuables. To me, that says it’s not really a good fit for a primary security system, Although you may find it useful as a secondary.
https://www.smartthings.com/guidelines/
Data accuracy and consistency from SmartThings sensors, including those provided by SmartThings directly, resold by SmartThings, or supported by SmartThings, is not guaranteed.
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Therefore, you should not rely on that data for any use that impacts health, safety, security, property or financial interests.
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For example, because temperature readings may vary significantly from reading to reading on an individual device, between devices, or over time, those readings should not be used to control heating and cooling in environments where food spoilage, health risks, or damage to physical goods could occur.
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Alternately, presence data from SmartThings devices or mobile/Smartphones can vary in accuracy, and therefore should not be used to control access to secure locations without secondary authentication.
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SmartThings provides information on the physical state of many devices, including through contact sensors (which may provide open/closed status of windows and doors), accelerometers, locks, appliances, HVAC, light and power fixtures, and presence sensors.
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The complexity of combining physical interactions with digital interactions may result in inconsistencies in the representation of the actual state of a device in the physical world in its digital representation.
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In all cases, SmartThings does its best to interpret and maintain the state of these devices (including by querying for current data), but this is not intended as a replacement for direct, physical verification in situations where the true state of a device may have an impact on health, safety, security, property or financial interests. For example, you should not assume that a curling iron (which may cause a fire if left on too long) is actually off without physically verifying the state.