BillGuard is a new service that polices your credit card activity for unwanted or unauthorized charges. In addition to numerous automated tests, the service also monitors online customer complaints about suspicious charges or merchants and flags any similar charges found on the credit cards of its users (see their intro video).
BillGuard scans your card activity daily for hidden charges, billing errors, forgotten subscriptions, scams and fraud, and alerts you via email when your attention is required. Each new transaction is analyzed by over 100 automated tests. BillGuard also scours the web for complaints posted by others about similar charges and merchants that appear on your bills.