Use someone else's secondary card. Does he know your information?

Partly. Using someone else's secondary card, the user of the primary card can view the call records and SMS records of the secondary card, but viewing the private information of the secondary card, such as address book and photos, requires special settings and permissions. In addition, the main card user will receive a real-time reminder of the consumption information of the secondary card, so he knows some information about you with someone else's secondary card.