The Threat Scope is the name for two different kinds of attachment in Titanfall 2. They both take the form of optics providing an AR overlay on their scopes, highlighting enemy troops in red.
However, the main difference is in size; assault rifles, SMGs, Light Machine Guns and shotguns all get one that is more comparable to a Holographic Sight, while Sniper and Marksman weapons get a full scope. Every single primary weapon, with the exception of the Grenadier class, has compatibility with one variant of threat scope or the other.
Due to the power offered by highlighting enemies, Threat Scopes also take up the second mod slot for their weapon, meaning a Pilot must choose between having two mods and another sight, or a single mod and the Threat Scope.
The Threat Scope makes its return in Apex Legends, however in a form of a legendary item, which means that it can either be found only in care packages (4-10x Sniper Scope), or rarely can be found on ground (1x Threat Scope). It can no longer be equipped on LMGs or assault rifles anymore; however, players can put this attachment on pistols and the Charge Rifle.