许多联邦的居民也对学院的合成人充满了偏见与猜忌，担心自己可能会被学院杀害并被用合成人替代。可怕的是，他们猜的没错。很多合成人间谍都表现的天衣无缝，足以骗过不知情的人。There are some examples of Commonwealth citizens that were murdered and replaced with synth duplicates whom the Sole Survivor interacts with on missions if they choose to join the Institute.
一，二代合成人的智能与三代合成人相比要低得多，很多都是编写出来的，例如在战斗中它们会对目标说“无论你是谁，我都知道你在这”。在他们追丢目标的时候则会表示他们的系统需要重新校准。During the Tradecraft quest, 迪根会表示一二代合成人与保卫者和其他戰前机器人的心智水平没有区别，并引起其他鐵路組織成員是否该解救一二代合成人的辩论。
有着从实验室培养出来的骨骼、血肉与器官，三代合成人无论是生理还是心智都与人类区别不大，除了杀掉合成人之外也没有办法通过医学方式鉴定一个人是否为合成人。 As Dr. Roslyn Chambers found, no medical tests or procedures can identify someone as a synth without killing them (synths that infiltrate settlements, for example, only drop synth components when killed). Psychological tests, such as Covenant's SAFE test, are dubious at best. 然而三代合成人仍然不是完美的，仍然与人类有一些不那么明显的区别:它们的身材不会发生变化，而且还很喜欢吃蛋糕。
There are many Generation 3 synths that are hidden in plain sight in the Commonwealth. They include, but are not limited to, Magnolia, the singer of the Third Rail and Danse, a paladin of the Brotherhood of Steel.
While most Synths are Gen 1 or Gen 2 and are thus allied to the Institute, synths can also be encountered in other places.
在游戏中，玩家建立的广播站吸引来的居民里就可能包括合成人，如果这些合成人被放到刚好路过兄弟会据点的补给线上，他们会被兄弟会攻击, stalling any building the player character can do. [需要引证]
在僅存者收回城堡之后and has an ample amount of well-off settlements，合成人也有可能会加入到义勇军巡逻队，但这些合成人路过兄弟会据点时不会被攻击。Sometimes their patrol routes take them straight through the Boston Airport, into the courtyard of Fort Strong, and back through again. They will not fire upon each other and will sometimes pleasantly engage in dialogue with each other. [需要引证]
玩家与学院交恶时(in other words, completed the quest Banished from the Institute)合成人居民将会更频繁的出现，玩家招募的合成人会袭击其他村民。
Synths often come in groups of four or so, armed with Institute weapons. Like ghouls, their limbs can be removed without killing them, and they will adjust their tactics accordingly.
Stronger than an ordinary synth, these striders, while fairly weak, are still a significant step up. They, like their counterparts, almost exclusively use Institute weapons and in some instances, shock batons.
A step up from the synth strider and leader variants, the patroller is stronger and has better aim. They are usually seen in groups with other synths, such as synth striders or leaders, and are usually seen with Institute pistols or rifles.
In Fallout 3, the synths are known as "androids." Records on Father's terminal give an explanation for the name change.
After a synth's destruction, one can observe their eyes still moving around, despite having been defeated. This seems to stop after decapitation.
Synth models as early as Nick Valentine and DiMA can smell.
Gen 1 and 2 synths are affected by the Troubleshooter's legendary prefix, but Gen 3 synths are affected by the Assassin's prefix.
Synths appear in Fallout 3 and Fallout 4. The two synths encountered in Fallout 3, Armitage and Harkness, were ostensibly Generation 3 synths, and Generation 1 and 2 synths were not introduced until Fallout 4.
Synths share many similarities with the terminators from the Terminator film franchise. One is that the Generation 1 synths are nothing more than endoskeletons that loosely resemble a human skeleton, just like the majority of terminators created by SkyNet. The Generation 2 synths differ in that they possess artificial skin like the T-600 terminators shown in Terminator Salvation. The Generation 3 synths were designed to look exactly like human beings so that they can infiltrate human settlements undetected, which is the exact purpose of the T-800 infiltrator seen in every Terminator film. Sometimes when in combat with Gen 1 and Gen 2 synths, they will say to the player character "You must be terminated." Finally, the biggest similarity is that both the Fallout and Terminator franchises depict a post-apocalyptic America destroyed by nuclear war.
The Generation 3 synths are quite similar to the Replicants from Blade Runner, based on the novel Do Androids Dream of Electric Sheep?, in that they are synthetic humans genetically engineered entirely out of organic substances and are virtually indistinguishable from real human beings. The author, Philip K. Dick explored ideas of different types of conscious beings as equal with humanity, and the human reaction to these rival sentient beings. This is one of many Blade Runner references throughout the game. In fact, the surname "Deckard," if used in some way as part of the player character's name, is one of the names that Codsworth is capable of saying. This is a reference to Rick Deckard from the film. In addition, the test required to enter Covenant measures psychological response to random questions, very similar to the Voight-Kampff test that Blade Runners give suspected Replicants.
The hunting of rogue synths somewhat references the movie Artificial Intelligence. The movie depicts a futuristic America where androids are used as servants for various jobs, but they commonly gain self-awareness and run away only to be hunted down and destroyed.
The exact distinction between Gen 1 and Gen 2 synths is a little vague. In the games files, there are three types of non Generation 3 synths, not two. Some are unambiguously Gen 1 synths and spawn with a completely exposed mechanical skeleton and typically do not use armor, as seen in Kellogg's memories during Dangerous Minds. On the other hand, some are unambiguously Gen 2 synths and have intact "skin" which can only be damaged by crippling their limbs, expressive faces, and typically wear clothes, such as the synth requisition officer. In between these are synths with rigid plastic skin, which typically spawn at least partially damaged and can be blasted off by the player character even without crippling limbs, similar to other robots. The last group could represent Gen 2's that have begun to decay, but given the more rigid appearance of their skin, they appear to be an earlier model. It could be that Gen 1 synths may have been built with plastic casings that often degraded over time and some units simply have none left.
Gen 2 synths bear similarities to the NS-5 robots from the film I, Robot.
Synths may be based on Star Trek's Androids. Both have human variants such as Data and Gen-3 Synths. There is controversy on what to call them, androids or synths, synths being short for synthetic humans. Both have controversy as to whether they are people or not, as Data, at one point, was threatened to be dissected and used to create more, saying he is not a person. Synths have the Railroad and East Coast Brotherhood of Steel, and they both have someone they call Father, for Data it is the scientist who created him and Lore. For the synths, it is Shaun, who was essential in creating 3rd Gens.