Mesmetron

The Mesmetron is a prototype stun gun in Fallout 3.

Background
The Mesmetron is an experimental pre-War "non-lethal pacification" weapon that was being tested in the months immediately preceding the Great War. It operates by sending a signal pulse into a human target's brain that scrambles higher-level mental functions, leaving the target extremely susceptible to suggestion. Still in its testing phase, the weapon was found to have the potential to trigger two undesirable side-effects: extremely increased aggression, or spontaneous cranial eruption.

Characteristics
When used on the specified quest non-player characters, it puts them into a hypnotic stupor, allowing the player to rob and enslave them (by putting a slave collar on them) and send them to Paradise Falls. It also appears to work on many other non-player characters (aside from quest related ones), but can simply send them into a berserk frenzy in which they become hostile towards the player and every other non-player character in the area. Occasionally, victims will run several steps before their heads explode.

It uses Mesmetron power cells as ammunition. You start out with 50 Mesmetron power cells. Grouse will also sell you additional power cells, but at the fairly high price of 200 caps for 10 power cells. This gives you the opportunity to make an additional 2500 caps every time you purchase more power cells (provided you successfully capture all 10 slaves). An additional 71 Mesmetron power cells can also be found in the Underground Lab in the Point Lookout add-on.

The Mesmetron can fire a total of 2475 waves, or 495 full cells, before breaking.

Using the Mesmetron
As previously mentioned, using the Mesmetron on an non-player character can have 3 different outcomes. These effects vary and are generally unreliable, so it is advised to save before using this weapon on anyone important. Due to the fact that using the Mesmetron is considered assault, it is advised to "mezz" someone while not detected (Stealth Boys and the Chinese stealth armor will come in handy here). Be aware that mezzing anyone who is already wearing a slave collar will cause the collar to malfunction and explode, killing the victim. Hostile non-player characters who were mezzed can also be turned friendly by being freed by the player (high Science skill required). An analysis of the Mesmetron's effects:

Mesmerize/Stun (50% probability)
This effect stuns the target for a few seconds, during which time the victim will stand with his/her head swaying from side to side and it is possible to engage them in conversation. Some characters cannot be stunned, in which case the probability of the Frenzy effect is raised to 80%.

While in conversation, you will first have three options: The first convinces the character to allow you to take his/her things (by either telling them it's a magic trick, that there is a thief on the loose, that you think they stole something from you, or by just telling them to give you their things) and will open up the victim's inventory (even what he or she is wearing/using), allowing you to remove or add any item. The second slips a slave collar on the character (instantly netting the player negative Karma). The third simply tells the victim to "walk it off"; this will exit the conversation and make the character resume what they were doing (assuming you haven't made any onlookers hostile).

The second set of dialogue options is unlocked by slipping a collar onto the victim: The first is the "cruel" way to tell the victim that he is now a slave ("...your head will explode!"), the second option allows access to the slave's inventory, and the third option is a slightly friendlier way to inform the victim of his/her "new occupation" ("...nothing personal").

If the character is not spoken to before the stun effect wears off, he or she will become hostile to the player.

Frenzy (30% probability)
This second effect causes the victim to go into a state of frenzy, attacking anyone nearby (most likely the player), and causing all other characters to turn on them. The onlookers may also become hostile to the player if you are seen stunning the victim. This method can also be a reliable way to get rid of victims without attacking them or getting negative Karma. You can die from this, especially if one of your enemies has any high-damaging weapons.

Spontaneous cranial eruption (20% probability)
This final effect of the Mesmetron may not be the most useful, but is definitely the most spectacular. When victims are affected by the Mesmetron in this way, they will become hostile (and either run, stand still, or attack) for just a moment before their heads literally explode. This effect will instantly get the player negative Karma (if the victim was good/neutral) and make any nearby non-player characters who were not hostile to the victim become hostile to the player.

Variants

 * Microwave emitter - A similar weapon designed for killing targets as opposed to stunning them, found in the St. Aubin Medical Facility at Point Lookout.

Location
The Mesmetron is given to you by Grouse, the Paradise Falls entrance guard, when you start the quest Strictly Business.

If you don't want to take the quest, you can obtain the Mesmetron by killing Grouse and looting his corpse. You have to kill him to obtain the Mesmetron, as it cannot be pick-pocketed. If you do this, you cannot get a slave collar and thus can't enslave non-player characters. You can still use the Mesmetron to frenzy or stun and rob non-player characters.

Related quests

 * Strictly Business

Bugs

 * Freshly enslaved NPCs will often be reported by Grouse to have died once the Lone Wanderer arrives at Paradise Falls. This is caused by a condition in the Mesmetron effect script which automatically moves the slave to Paradise Falls—indirectly marking them as dead in the process—once the NPC is no longer being actively rendered.  Aside from leaving the NPC's immediate vicinity, numerous actions have a random chance to cause an NPC to stop being rendered, including accessing the Pip-Boy, facing away from the NPC for a certain period, or even accessing the game menu.
 * A third-party bugfix has been released which addresses this issue: Mesmetron and Enslavement Fixes at Fallout 3 Nexus
 * Attempting to remove a collar from a non-player character enslaved by the Lone Wanderer (other than Susan Lancaster, Flak, Arkansas, and Red) can result in a crash to desktop, depending on the non-player character's actions immediately prior to the conversation. Crashes seem more likely to occur as the time between enslavement and collar removal increases, but are less likely if the enslaved non-player character is not on their usual route.
 * Removing a collar from a non-player character who was mezzed while in combat may cause them to die once the collar is removed. This seems to happen more often (but not only) when the non-player character was stripped of their armor and/or at low health before being mezzed. The non-player character's death does not appear to be attributed to the player and will not give XP.
 * "Mezzing" characters who are seated, leaning on a wall or lying down may cause them to spin rapidly in place before their heads explode.
 * When you untie a captive and then use Mesmetron while he or she is getting up, the person will be stunned and not be talkable. When the stun effect passes, the person will still appear to be tied but can no longer be engaged in conversation.

Sounds
Гипнотрон