The Bio-Mask is one of the main tools used by the Yautja. As well as performing the basic function of protecting a Predator's head, the mask also grants the wearer access to multiple vision modes including zoom capabilities, facilitates Vocal Mimicry, and includes breathing apparatus, diagnostics, and visual and audio recording systems. The mask often also incorporates a red targeting laser used in conjunction with a Plasma Caster.
The Bio-Mask is directly linked to a Predator's Wrist Gauntlet, which controls many of the mask's functions. Together they form one of the most versatile tools used by the Predators, while the mask itself is a distinctive aspect of their overall appearance.
The Bio-Masks were shown to have access to several different visual frequencies, is most commonly seen being infrared, effective to visualize the humans, but useless in a Xenomorph Hunt. Also available is a spectrum and a specifically tuned mode, EM field detector, used to visualize Xenomorphs. Additional vision modes are available to determine the health status of the targets. In Alien vs Predator : Requiem one yautja gathers the substance he was containing a Facehugger in and installed a new vision mode on his Bio-mask which allowed him to see the substance highlighted. He did this by inserting the substance via a needle into his Wrist Gauntlet, suggesting a connection between the two.
Housed within the helmet is a targeting and tracking system for shoulder based Plasma Casters. A shoulder mounted Plasma Caster uses this laser target designator, which comprises three corners of an open triangle, to aim at the designated prey. Incorporated to finalize the shot is a lock-on system. As the quarry is decided upon, the designator will zoom a triangle in on the prey which will flash and turn solid red, then fires. This also has a zoom capability, so the Predators can see and aim over great distances. This tracking system also allows the Predators to plot trajectories of thrown objects. The targeting system can also be used to heat up metals like Wrist Blades.
Another feature of the Predator's mask is its voice translator/recorder. This device can both record and play strips of audio, which a Predator may use to express meaning or catch prey off guard, or to simply listen to the voices of their prey, as if to study their language. The mask also seems to affect hearing as well; in Predator, when the Predator took its mask off, it heard things at a much higher pitch than before and slightly more distorted. As seen in Aliens vs. Predator: Requiem, the helmet also has a video playback mode that displays what the wearer has witnessed or been involved in.
In the Aliens versus Predator video games, the Predator has four vision modes, regular vision (to fit in with the first-person shooter genre), thermal (spotting regular beings like humans), electric (gives a red background, used spotting Xenomorph's by their white outline), and Predator vision (gives a green background, used for spotting other Predators and technological objects, such as weapons and armor, shown in a white outline).
However, in Aliens vs. Predator, there are only three Predator vision modes: Normal, Thermal/Heat, and Xenomorph. Normal mode is self-explanatory. Thermal vision is used to detect humans and Synthetics (and Predators — cloaked and uncloaked — in death matches). Alien vision is to detect Xenomorphs. humans, Synthetics, and Predators (especially cloaked ones) are nearly invisible in Alien mode, whereas Xenomorphs are nearly invisible in Heat mode.
In Predator: Concrete Jungle, the Predator's mask offered four types of vision and varying diagnostic functions for each: Normal Vision, which was the same as a human and had no diagnostic; Thermal Vision, which highlighted heat signatures and could analyze health and armour weaknesses in prey. Although in this game it could also highlight Xenomorphs even though in the movies and games they are not seen in Thermal; Tech vision, which contrasted energy sources and analyzed a prey's weapon systems; and Neuro Vision, which exposed the prey's current emotional status (calm, panicking, hostile, etc.) and, on scan, would show the target's affiliation and rank.
There have been numerous Bio-Mask designs and variations shown over the Predator franchise.
City Hunter's Bio-Mask: This mask was similar to the original one, but instead of two eyeholes, there was one visor and it was a different color and shape than the original.
Chopper's Bio-Mask: This mask had gill-like patterns on both side of its mouth area and a single visor. Because of this design, Chopper has also been called Gill.
Scar's Bio-Mask: This mask was in many ways identical to the Jungle Hunter's mask, although it had a City Hunter-type visor. However, when Scar kills his first Xenomorph, he burns a mark onto the forehead, marking him as a Blooded Yautja. This mark is revealed in the AVP commentary to be a Xenomorph.
Wolf's Bio-Mask: This mask had marks all over it, and there was also, on the forehead, a reptillian hide over it, complete with spikes. The mask bore a strong resemblance to the City Hunter's mask though it had two eye-pieces rather than a single visor.
Tracker's Bio-Mask: This mask looked similar to the normal Predator mask, but it had two tusks strapped to it.
Falconer's Bio-Mask: This helmet was somewhat bulkier than others. It had lines on both sides of the mouth area, and also had two metal spikes on the back. It slightly resembles a real-world falcon head.
Berserker's Bio-Mask: This helmet had a jawbone it. Its design was more narrow than the mainstream Predators and was darker in color.
Crucified Predator's Bio-Mask: This Bio-Mask is almost identical to the one used by the original Jungle Hunter, although there seems to be damage on the left side of it, exposing the Crucified Predator's left eye.
Serpent Bio-Mask: This mask appears to be styled to represent the face of the Aliens. The forehead is smooth like that of the Alien and the mouth area is shaped like the fanged maw of the Alien. It also has a split crest at the top.
Spartan's Bio Mask: This mask is shaped like a spartan helmet only this helmet is a little more high tech. It has somewhat of an opening near the mouth and has two visors just like a real spartan mask. It is also split into three sections at the top of the head.
Elder Predator Bio-Mask: This mask is a lot different than the other Predator masks. It has an opening near the mouth area & it has two visors with a lot of writing and markings on the top of it from all the battles it has experienced.
Ancient Predator(Bull) Bio-Mask: This Helmet appears in Sebastian's Story to Alexa about first Predators coming to Earth. First, it appears in the first scene, where humans climb the Pyramid and bow to the Predator who is observing the other Mother Ships landing. Next, it appears in the last scene of the story. The middle one of the three Predators expands his spear, and as the camera moves backwards, the front area can be easily seen wider and concave. Next, it can be seen in Aliens vs. Predator: Requiem. After the Predalien killed a Predator in the trophy room of their Mother Ship, the commander of the ship (Bull) is seen wearing his mask, and there is a close-up of it.
Big Red's Bio-Mask: This Helmet appears in Dead End fan film. After Batman defeats the Predator, the hunting party appears led by Big Red Predator. The mask he wears is almost the same as Jungle Hunter mask, aside the fact its in red coloration and has black ornaments on forhead.
Scarface's Bio-Mask: This helmet appears in Predator: Concrete Jungle. It belongs to Scarface and bears a striking resemblance to Celtic's Bio-Mask. The only real difference between the two is that Scarface's Bio-Mask has a row of pointed spikes in the middle of the mask and a red line going down the left eye hole.
Aliens vs. Predator Bio-Mask: This mask appears in the 2010 video game Aliens vs. Predator and its worn by the Elite Clan students as well as Dark himself. It bears resemblance to one that was worn by the Jungle Hunter. However it has row of vertical patterns on each cheek and it's somewhat darker than the other masks.
The Predators use an infrared vision made in their masks as their primary source of vision. This gives the Predator a thermal imagining sensory where they use it to track, survey, and target their prey. However, in the original theatrical release Predator, this can be skewed by the prey when Alan "Dutch" Schaefer becomes covered in mud, which covers his heat image, thus allowing him to hide not but a few feet away from the Predator. Dutch realizes this and uses it to work to his advantage later in the final battle.
Predators also employ an ultraviolet vision mode, as seen in Predator 2. However, it is shown that during this scene we see the City Hunter employ several different modes of vision before settling on one. Not all of these vision modes are known.
During the theatrical release of Alien vs. Predator, we also see that the Predators have what seems to be a finely tuned EM Field Generator, which is used to see and hunt Xenomorphs, since infrared is seemingly useless because Xenomorphs don't give off any heat, and acid doesn' generate heat. In this vision mode we see the Xenomorphs as a green outlined figure, more or less.
In Predator: Concrete Jungle apart from the thermal vision there is a vision which shows electrical currents and a neural vision which shows the mood of the Predator's prey, allowing the Predator to tell the difference from passive civilians and aggressive enemies.
In Aliens Vs Predator Deadliest of the Species, the masks are shown also as working as a life support system, allowing the Yautja to breath easily on any world, (The Yautjas can also breath on human worlds, but have more difficulty, having to breath deeper.) It also featured a modified version allowing a human to breath in a natural Yautja environment, which would normally burn the lungs of and kill any human. Though this conflicts with Predator 2, where a human walked around unaided in a Yautja ship without being harmed at all. In the first Predator film the mask was originally designed to look like a mechanised version of the creature's face. The prop was scrapped, as it was felt that it gave away the Predator's final appearance too early. The original design would reappear in subsequent films as the helmets of background or secondary Predator characters. In Aliens vs. Predator: Requiem, concept artist drew the helmet of the Wolf Predator as being made from a trophy skull, while drew the mask as identical to that appearing in Predator 2, with the addition of a spiked reptilian hide strapped to it.
In Predators, it seems to show that Predator masks are capable of withstanding incredible damage. The Crucified Predator seems to have had part of his helmet blown off by from the blast mark of presumably a Plasma Caster more than likely Mr. Black's before the events of the movie, as it seems to be functional when Classic puts his back on. Also, in Aliens vs. Predator: Requiem, Wolf manages to gain knowledge of the Predalien through the mask which seems to have had the top stabbed through. This may also mean that Celtic's helmet, while punctured, if been recovered, may have very well worked. Although this can also mean that most of the technology to work the mask is in the mouth area which makes sense as the others are still functioning and with battle scars to the forehead or face.
A Yautja's Bio-Mask has the ability to flash its eye area, turning them usually bright yellow. In Predator, the Jungle Hunter does this while he's staring at Mac. In Aliens vs. Predator, as Rookie in the jungle mission, after you find the skinned body, you can just notice a Yautja walking past you while flashing its eyes. This happens again in the Alien mission (The Ruins) where you fight the Predators, but the Predators' eyes flash bright green, not yellow. Wolf also flashes his eyes blue. This is most likely customization by the Predators. They could possibly use this visor-flashing ability for frightening or intimidating their prey to make them run. This would make their quarry easier to kill as said by Royce that if you run, you die. It is also possible that Predators do not flash their eyes intentionally, but it is rather a side-effect of the Cloaking Device. Since the field bends light around the Predator, the Predator would not be able to see, since visible light, and thus potentially infrared light, would be bent around the Predator's eyes, preventing it from reaching them. The area around the eyes may have a "weakened" light-bending field or some other mechanism to allow light to reach the Predator's eyes, resulting in the eye lenses of the mask seeming to "flash" at certain times or angles.