You can add professional monitoring to a standard smartthings system with Noonlight. But remember that it is completely dependent on the smartthings cloud. If the cloud is unavailable, your Internet is out, or your power is out, the monitoring center will not be notified.
So it’s a step up from just self monitoring, but it’s not comparable to a purpose built security system like ring or abode.
Also, at present it must be set up with the classic app although it can then be used in the new V3 app. And the classic app will be discontinued in a few months.
Some relevant discussions:
[OBSOLETE] Professional smart home monitoring for security and smoke alarms with Noonlight
As of this writing, the cost is $10/month, the same as ring, but with fewer features since there is no cellular backup.