The sonic emitter - Gabriel's bark is an Energy Weapons pistol with bonus damage against robots and power armor wearers, as well as a unique "critical strike knockback" effect, knocking enemies down on critical strikes. This sonic emitter is named after the cyberdogGabriel, and the holodisk containing the upgrade is found in one of Gabriel's digging spots. This sonic emitter modulation has a burgundy oscilloscope.
Sometimes, after entering the testing area and killing Gabe, leaving while the think tanks are still talking, then returning to the testing area and acquiring the Gabriel's Bark holotape, even though the holotape was picked it up, it is missing from inventory. [verified]
In some playthroughs, Audio Sample - Gabriel's Bark will not spawn in any of the digging spots and there is no way to get the holotape to re-spawn through a previous reload or otherwise. [verified]