A circuit board with several unidentifiable parts, a microphone, and an inscription that reads "Vault-Tec Voice Recognition Module."”— In-game description
This is a snap-in module that fits in the computer in Vault 13.
You can buy it from Eldridge in Reno for $3000 ($2500 or $1500 if you try to haggle enough) or you can find one on the second floor in Vault 8 (Vault City). By fixing the computer, Gruthar and the talking deathclaws give you their GECK.