Its sophisticated surveillance technology makes it easy for the Party to control it citizenry. The telescreens that can never be turned off and which broadcast into private homes are two way: they can both be watched and used to watch others. Nobody knows at any given moment if they are under surveillance. This threat of the panopticon or all seeing eye is enough to cause people to self-regulate and self-censor:

You had to live—did live, from habit that became instinct—in the assumption that every sound you made was overheard, and, except in darkness, every movement scrutinized.

The Party also has the ability to vaporize people so that any trace or memory of them is wiped out of existence. Winston's job, in fact, is to rewrite history, in part in order to expunge the record of anyone considered undesirable. These people are whisked away into the Ministry of Love, where advanced torture technology through drugs and machinery make it possible to remold a person's thinking and allegiance to the state.

Surveillance even extends into Prole territory: Mr. Charrington is actually an agent of the secret police and the apartment over his shop that Winston and Julia rent is bristling with surveillance equipment.

However, all this surveillance technology is enhanced by the government's ability to convince Party members to spy on each other and report any deviance. Were people to rebel and refuse to collude with the government in surveilling each other, the Party would have a harder time maintaining control, despite its technology.

The rules of the dystopic society of 1984 utilize both the actual technology and the threat of using it to control the citizens. Everyone believes the slogan “Big Brother is watching you” because it is generally true. Fear of surveillance is promoted by the selective and intensive use of technology; people believe they are always being watched and heard because the devices are often visible. Belief that even their thoughts are detectable and subject to punishment (for “thoughtcrime”) also encourages obedience. The most powerful device and symbol is the ubiquitous telescreen. People who assume that they are not being watched do so at their own peril, for hidden devices may be present anywhere.

Technology is also used to alter facts so that people are never fully informed about current events. Workers such as Winston in the Ministry of Truth physically manipulate the incoming information, changing it to fit with the Party’s priorities. Using the “speakwrite,” the worker rectifies documents that are at odds with the dominant ideology. The old documents are destroyed.

In 1984, technology makes it easy for the Party to control its citizens. The telescreen, for example, enables the Party to keep a constant watch over the people of Oceania. Not only can the telescreen see every citizen's actions, it also records every single conversation, ensuring that citizens maintain total obedience to the Party.

Moreover, by placing hidden microphones all over the city, the Party can monitor citizens wherever they are and act swiftly if a person is caught breaking the rules.

In addition, through the use of memory holes, the Party can destroy any pieces of literature or photographs which do not portray it in a positive light. We see this clearly through Winston's work at the Ministry of Truth. His job is to rewrite history to make the Party always look correct and benevolent. By doing this, the Party controls and defines all knowledge in Oceania, which makes it easy to psychologically manipulate the people.

As was mentioned in the previous post, the most prevalent piece of technology used to control the population in 1984 is the telescreen. Telescreens are placed in each home and allow the government to continually monitor citizens' activities. The telescreens function as a video camera, as well as a loudspeaker that issues Party propaganda. The government also employs miniature microphones throughout the country that listen to people's private conversations. Surveillance technology makes it difficult to collude against the government, and constant Party propaganda manipulates the minds of the citizens.  

The Party also continually rewrites history using sophisticated devices that allow Outer Party members like Winston to rewrite and erase articles. Altering history allows the Party to create the impression that they are always right in the eyes of the public.

At the end of the novel, Winston is captured and tortured in the Ministry of Love. Although Orwell does not specify the details of O'Brien's torture device, this technology allows the Party to effectively brainwash the minds of rebellious citizens. It is also a deterrent that discourages citizens from plotting against the government. 

The concept behind 1984's powerful Party is its ability to control its citizens.  They adopt a plan of fear and manipulation to do so.  At the center of this plan is their technology.  Telescreens represent Big Brother's invisible eye on all the citizens who are required to keep a telescreen in their homes.  In addition, the people are constantly under the eye of the telescreen in public, at work, and even at social functions.  

For the few times that telescreens are not available, voice-recognition microphone bugs pick up the conversations of those around.  However, Winston and Julia learn that hard way that just because you do not see a telescreen, it doesn't mean one isn't there.  They are captured because a telescreen was hidden behind a picture.  

In addition to the constant surveillance, the Party continually manipulates the people's thoughts.  Winston works for the Ministry of Truth, which specializes in the daily rewriting of history.  Anything the Party wants to rescind or reconstruct occurs in an instant.  Winston simply makes the changes electronically to all the known sources of information.  The people's beliefs about war or food rations are changed so quickly that nobody knows what to believe, and for their own safety, concedes to the truth the Party creates.

The Party uses two-way telescreens to spy on people.  The telescreens are positioned in people's homes, as described in Part 1, the first few chapters, so that most of the area is visible to the camera.  This gives people few places in which they have privacy.  The Party shows programming on the telescreens such as exercise programs and political rhetoric but it also can see into the rooms.  The telescreens aren't just in people's homes; they are everywhere such as restaurants, bars, any place where people might be.  Additionally, there are hidden microphones and people never know when the Party might be listening or watching everything said or done.  Even if no one is currently watching or listening, the people don't know when the Party might be and they have to assume that they are always under surveillance.  This constant fear of being watched allows the Party to control the population.  People see enough instances of others being taken away by the Party, never to be seen again, to have cause to constantly worry about their own well-being. This fear makes the people easy to control.