The headset in Universal Soldier is one of the most distinct identifying qualities of the franchise. The primary components of the headset are a camera for remote viewing, an eye piece (or view finder), an ear piece and a microphone. The headset has evolved substantially since the beginning of the franchise,
The headset in the first Universal Soldier is the archetype that the subsequent models were based off of. The headset was a tool that was used to give the GR units direction and to be able to see what they were seeing remotely and in real time. For the early 90's the image quality of remote video wasn't bad, but it wasn't sharp either. The first model UniSol headsets had targeting capabilities as well as being able to identify firearms. The movies suggest that the headset reports data back to the computer on the truck and has no real or random access memory of its own. These headsets are not attached.
Universal Soldier II & III (Non-Canon)
The headsets from the non-canon Universal Soldier movies are practically identical to the ones from the first film and have no advancement over the original models.
Universal Soldier: The Return
The headsets in US:TR (worn by the 2500 Series UniSols) are much more aerodynamic and functional than those worn by the original UniSols. The visor encompassed both eyes instead of just one and were much lighte, resembling sunglasses though suggested to me made of a much stronger substance. The camera was a pin dot camera (similar to covert cameras used in surveillance) and the feed was relayed directly to S.E.T.H.'s video banks as opposed to a computer monitor to be viewed by a user. It is suggested that S.E.T.H stores the data from the camera to be used to analyze training missions. The audio piece is completely independent from the visor and the whole assembly is worn during cooling periods where the first models were not worn during the cool down. This suggests that the headsets are all-weather type equipment. The 2500 series headsets had much greater targeting capabilities and clarity than previous models.
Universal Soldier: Regeneration
The headsets in US:R were worn by the Black Tower UniSols and were a retrograde from the US:TR models (it is understood that US:R retconned US:TR and completely removed it from continuity). The headsets were hardly less cumbersome than those worn by the original line UniSols. The eyepiece was mounted directly over the left eye as opposed to being attached to an auxillary assembly and the camera had high-definition capability. These headsets included a new feature: rear view. A camera was mounted in the back of the headset to give the command center a view of what was behind the UniSol. It is unclear if the UniSols themselves were able to take advantage of the feature. The auditory parts wrapped around the side of the head and the headsets were actually secured to the soldier via being bolted into the skull. It is suggested that the headsets are biologically powered as the camera feed cuts as soon as the UniSol user is deceased.
To date there have been no officially licensed replicas of the UniSol headset. There is a picture of one made independently on the internet but it is not listed for sale.