I'm pretty sure that depends on who issued your card.

Visa has a zero liability program for debit card - http://usa.visa.com/personal/security/visa_security_program/...

These are the FTC's rules [1], I'm not sure if Visa or Mastercard can make them 'better' (give you a larger window). They have an interesting tidbit below their chart -

>If someone makes unauthorized transactions with your debit card number, but your card is not lost, you are not liable for those transactions if you report them within 60 days of your statement being sent to you.

Isn't it free to get a new card? That'd be the easier way than worrying.

[1] http://www.consumer.ftc.gov/articles/0213-lost-or-stolen-cre...