We know how much you value your health data, which is why starting in Zero 3.0 we enabled cloud syncing of all your Zero data. This article covers how we store your data, including how we protect your data.
When you create an account with Zero, all of the data you add or sync to the app will be stored in the cloud. Specifically, we use Google's cloud storage, which is certified under major privacy and security standards including ISO and SOC. All of your data is encrypted during sync using HTTPS, and also when it sits on Google's servers. These measures help ensure that your data is secure.
To dive deeper, you can visit Google's Firebase FAQ for privacy and security here.