PainChek stores some data on your device. This is not the main copy of the data (which is securely stored and backup on our servers) and so it doesn't matter if your device fails or is lost.
However, in order to completely secure that local data, it's necessary to encrypt your device.
On iOS devices (running iOS 8 or later), encryption is enabled when you set up a device passcode (that is a passcode that you need to enter to unlock the device).
On Android devices (running Android Gingerbread 2.3 or later) this is achieved by enabling encryption (go to Settings and then Security) and check to see if your device is already encrypted. If not, enable it.
It is also recommended that you have a PIN, password, or pattern on the lock screen to further boost the security. A strong passcode (6 or more random characters/numbers) is recommended.
It is industry best practices to recommend encryption for all devices and it is beneficial, not just for PainChek data, but for all data your device.