The NSA Incinerator is a remote detonated explosive "designed to eliminate all biological traces" disguised as a mobile phone, seen during the episode "Chuck Versus the Helicopter". It was developed by the NSA, but it is supposedly easily obtainable on the black market.
The Incinerator is activated by phoning the device, and is used by Dr Zarnow to fake his own death, prompting Casey and Sarah, who at this point don't trust each other (due to the inherent mistrust between the CIA and NSA) to each believe the other was the murderer. The device appears again later in the episode, when Chuck has been convinced by Casey that Sarah is the traitor. The two sit down in Casey's car, when a phone call is heard. They instantly realize it is an Incinerator, and run before the car explodes; the two believe it was Sarah, when in fact it was a trap set by Dr Zarnow. The Incinerator is not featured again.