Some browsers or devices allow you to set up incognito/private browsing sessions or tabs that won't be tracked on the device. Other devices allow you to log in temporarily as a "guest" and remove data from the account after logging out. Circle can still track and manage the traffic even while using those features.
Circle and tracking incognito/private browsing
Circle sits inside your network it gets to manage all outbound traffic coming from a device. In Incognito mode, a private session/tab, or using a guest account won't stop Circle from managing that traffic. In addition to still managing it, you'll also get accurate reporting about Usage and History.