Mesmetron

The Mesmetron is a unique weapon 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 character 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 turn hostile to the Lone Wanderer 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, starting out with 50 power cells. Grouse will also sell additional power cells, but at the fairly high price of 200 caps for 10 power cells. This gives the opportunity to make an additional 2500 caps every time one purchases more power cells (provided all 10 slaves were successfully captured). An additional 71 Mesmetron power cells can also be found in the underground lab in the Point Lookout add-on.

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

Using the Mesmetron
As previously mentioned, using the Mesmetron on a 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 undetected (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 character (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 their 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, there are three dialogue options: The first convinces the character to allow having their things taken (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 they are wearing/using), allowing to remove or add any item. The second slips a slave collar on the character (instantly netting 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 no onlookers turned 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 they are 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 their "new occupation" ("...nothing personal").

If the character is not spoken to before the stun effect wears off, they will turn hostile towards anyone they can see, that includes the player character.

Frenzy (30% probability)
This second effect causes the victim to go into a state of frenzy, attacking anyone nearby (most likely the player character), and causing all other characters to turn on them. The onlookers may also turn hostile to the PC if caught stunning the victim. This method can also be a reliable way to get rid of victims without attacking them or getting negative Karma. This is dangerous, however, especially if one of the 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 turn hostile (and either run, stand still, or attack) for just a moment before their heads literally explode. This effect will instantly give negative Karma (if the victim was good/neutral) and make any nearby non-player characters who were not hostile to the victim become so to the player character.

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 the Lone Wanderer by Grouse, the Paradise Falls entrance guard, upon starting the quest Strictly Business.

If deciding not to take the quest, the Mesmetron can be obtained by killing Grouse and looting his corpse. It cannot be stolen from him, meaning he needs to be dead to get it. If this is done, it's no longer possible to purchase any mesmetron power cells nor slave collars from him, thus one can't enslave non-player characters. The Mesmetron can still be exploited to frenzy or stun and rob non-player characters, however.

Related quests

 * Strictly Business
 * Strictly Profitable

Bugs

 * Freshly enslaved non-player characters 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 non-player character is no longer being actively rendered. Aside from leaving the non-player character's immediate vicinity, numerous actions have a random chance to cause an non-player character to stop being rendered, including accessing the Pip-Boy, facing away from the non-player character 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
 * "Mezzing" characters who are seated, leaning on a wall or lying down may cause them to spin rapidly in place before their heads explode.

Gallery
Гипнотрон Mesmetron