A look at the post-Sept. 11 surveillance provisions that, barring a last-minute deal in Congress, are set to expire when Sunday turns into Monday:

Section 215 of the Patriot Act

This has been used to authorize the National Security Agency's bulk collection of domestic telephone records, although an appeals court ruled recently that the law could not fairly be read to support that program. The ruling was put on hold pending the debate on Congress. Section 215 is also used by the FBI about 200 times a year to obtain all manner of business records, including hotel bills, travel vouchers and Internet data relevant to a terrorism investigation. The FBI says that collection is extremely useful, though a recent Justice Department report said the bureau could not point to any terrorism cases cracked because of the program, as of 2009. If the program lapses, the FBI will have to go back to pre-Sept. 11 language that is much more restrictive.

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Section 206 of the Patriot Act

This authorizes "roving wiretaps" in national security cases. Commonly used in drug cases, such wiretaps allow the FBI to target a suspect rather than a device, to account for a suspect who discards phones to dodge surveillance. In the national security context, they are more often used in spy cases than terrorism ones, officials say. If this provision expires, the FBI would have to get a separate order for each communications device it wants to intercept.

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Section 6001 of the 2004 Intelligence Reform and Terrorism Prevention Act

The "lone wolf" provision has never been used. It is designed to allow the FBI to eavesdrop on a non-U.S. person who is not affiliated with any foreign power, including a terrorist group.