For true tamper resistance you need to have some way to actually detect tampering and erase the secrets, which usually leads to some battery-backed SRAM and ass

For true tamper resistance you need to have some way to actually detect tampering and erase the secrets, which usually leads to some battery-backed SRAM and associated tamper response circuitry. While there are some smart cards and smartcard-like HSMs (Fortezza comes to mind, but it uses the battery primarily for integrated RTC and seems to not contain any tamper detection mechanism) with integrated battery, common smartcards does not have battery.