Turns out you can read out the contents of DRAM from a laptop for anywhere from a few seconds to a few minutes after the machine is off. Blasting the chips with the contents of a compressed air can slows the rate at which data decays. Of course, you need access to the machine either while it is on or shortly after it has been turned off for his scam to work. The encrypted data on disk drives is also at risk with the right techniques, as the video on this pages shows.

http://chronicle.com/wiredcampus/article/2764/with-a-can-of-air-hackers-can-steal-encrypted-data-from-laptops?utm_source=at&utm_medium=en