verb:

1. the action of recording a lock on a secondary or engram. (HCOB 23 Apr 69) —n.

noun:

1. the first time an engram is restimulated is called a key-in. A key-in is merely a special kind of lock, the first lock on a particular engram. (SOS, Bk. 2, p. 29)
2. a moment when the environment around the awake but fatigued or distressed individual is itself similar to the dormant engram. At that moment the engram becomes active. It is keyed-in and can thereafter be dramatized. (SOS, Bk. 2, p. 136)