Officially, the TSA requires that travelers remove laptops from bags so they can be thoroughly screened without interference. Scanners look down on the items passing through them on the conveyor belt, and operators must have an unobstructed view of the laptop. Bags with separate compartments that store peripherals, power cords and the like interfere with this unobstructed view. The TSA reached out to bag manufacturers in 2008 in an attempt to inspire new designs that would be more checkpoint-friendly. Several bag makers responded. Certain bag designs that hold the laptop in its own compartment, separate from anything that would interfere with the view of the scanner, are permitted to pass without requiring the traveler to remove it.
Whether the laptop is in a permissible bag or scanned on its own in a bin, the TSA reserves the right to swab the laptop searching for bomb residue. These checks are termed "Explosive Trace Detection" tests, and they are used on all manner of carry-on and checked baggage, including laptops. There is no harm done to the electronics during such tests.
The TSA offers tips to travelers regarding battery safety, but there is no prohibition on extra batteries for laptops. Travelers are advised to keep extra batteries in carry-on luggage rather than checked baggage in the unlikely event of a battery fire. An accident in a cabin bag can be dealt with more quickly than one that occurs in the cargo hold. Further, the TSA recommends that batteries come from reputable manufacturers with a third-party inspection label from an organization like Underwriters Laboratories. An additional recommended safeguard is that the battery be packed in its own protective sleeve with tape over the contacts to reduce the risk of fire.
The TSA will never inspect the contents of the hard drive in a laptop during the screening process. TSA staff will not even turn the laptop on. The similarly outfitted Customs and Border Control department may inspect laptop contents or even download information during the inspection. This is a function of border security and it applied only to travelers entering the country, but even then, the possibility of a full hard drive inspection is slight.
