Attach read-only account
Track the balance of an account using its address, without injecting its private key into SubWallet.
Step 1: Open SubWallet and click on the account name on top of the screen. You would be directed to a list of accounts.

Step 2: In the account list, choose the "Attach account" icon.

Step 3: Choose "Attach read-only account".

Step 4: Enter the address of the account you want to track, then click "Attach read-only account".

Step 5: Enter password then click "Apply" to continue.

Your read-only account is ready!. If you repeat Step 1 to get to the account list, you would notice that your read-only account would be marked by an "eye" icon. You could change the account name following this guide.

SubWallet helps you identify your read-only accounts with the eye symbol as shown in the picture above, so even if you are creative when naming this account, you can still identify it. Please make sure that you are not in a read-only account if you want to make transactions.
Please note that in order to see your assets after importing your account, your would need to manually enable the networks you want to use & have assets on. Please follow this instruction to enable the networks you want to use.
SubWallet automatically enable Polkadot & Kusama networks for Substrate accounts, but you can disable them if you so wish.