In multiple instances in Star Trek: Voyager, this sequence of events happen:

  1. A character asks the Doctor how he is able to exist outside of the holodeck/sickbay
  2. The Doctor informs them of the mobile emitter
  3. The character disables or steals the mobile emitter

This is evidenced in these occasions:

  • Equinox; Captain Ransom's EMH (minus ethical subroutines) steals the mobile emitter
  • Revulsion; Dejaren, the pshyco hologram that killed his humanoid crew damages the mobile emitter

Among other examples.

From what I see, the Doctor has a couple of options:

  • Don't tell anyone about his mobile emitter
  • Conceal the mobile emitter (such as tucking the mobile emitter underneath his sleeve)

Why wouldn't the Doctor simply conceal the existance of the mobile emitter?

  • 16
    The Doctor's naivety. Sep 25, 2012 at 22:53
  • 3
    I guess his pride makes him forget all of the times he's been violated? Sep 25, 2012 at 22:57
  • The Doctor has concealed his mobile emitter before. Once was while undercover as someone else, but I'm pretty sure there were other times when it wasn't strictly necessary, but he did so anyway...
    – Izkata
    Sep 25, 2012 at 23:33
  • 1
    IMO the visible emitter is just some plot device to remember the viewer it's still the doctor with his old limitations and (dis-)advantages. From a logical standpoint, it probably would have been possible to simply hide it inside his body, which might even be able to shield it from some damage and direct access. But in the end it's just some plot device to open new possibility's for the Doctor as a character.
    – Mario
    Sep 25, 2012 at 23:53
  • 5
    @Mario To allow an AI-controlled hologram to hide its emitter within itself would be a horrible idea from a security standpoint - if the AI ever went rogue, disabling it would be a lot more difficult.
    – Iszi
    Sep 26, 2012 at 13:40

2 Answers 2


OghmaOsiris's comment about the Doctor's naïvety is probably the reason. The Doctor's original programming as an Emergency Medical Holographic program would not have included the concept of people taking advantage of him. He was always stored in the computer.

The addition of holographic emitter allowed him new unexplored mobility. No doubt he eventually learned to be discreet about his holographic emitter, but initially the thought of it being used against him probably didn't occur to him.

It seems that most artificial lifeforms suffer from this naïvety, as Data did as well.

...but his lack of understanding often created social obstacles. He fell victim to several practical jokes and had difficulty with social gatherings.

Much like Picard was a father figure to Data, Janeway was a mother figure to the Doctor:

As the journey went on, the two of them also began to develop an almost mother/son relationship, with The Doctor often coming to Janeway when he needed personal advice or information about how his program was developing, as well as consolation about any wrong decisions he had made in recent times.

So artificial life for the Doctor is a new thing, and he is slow to learn that people cannot be trusted.

  • 1
    Made even harder because the Equinox EMH should have been able to be trusted, because its origins were identical to his own...
    – Izkata
    Sep 25, 2012 at 23:38
  • Thanks for expressing into words what I couldn't, lol. Sep 26, 2012 at 5:20
  • 4
    Additionally, note the Doctor being extremely proud of his ability to leave the sickbay/holodeck. It's a form of emancipation similar to Data's emotion chip or even Geordy's VISOR.
    – bitmask
    Sep 26, 2012 at 8:26
  • 1
    The Doctor's original programming as an Emergency Medical Holographic program would not have included the concept of people taking advantage of him. I'd argue the opposite, to ease working with the EMH it would be logical to actually make them listen to nearly everyone.
    – Bobby
    Sep 26, 2012 at 21:19
  • The Equinox references should definitely be added to the answer. There's a bit at the end where Seven volunteers to help the doctor improve his anti-tamper protections.
    – T.J.L.
    Oct 24, 2019 at 13:38

Well, we have one answer on why the Doctor wears the mobile emitter on his sleeve.

In Spirit Folk, the Doctor is held prisoner (along with Harry and Tom) by holodeck characters. The Doctor was using his mobile emitter to avoid holodeck malfunctions.

One of the holodeck characters snatches the mobile emitter from the Doctor, which triggers an automatic transfer to move the Doctor to the holodeck. The holodeck character continues to hold/clutch the mobile emitter, with seemingly no effect.

Under hypnosis, the Doctor indicates that the character can transfer to the "Spirit World" by using the mobile emitter. The character puts the mobile emitter on his sleeve, and Tuvok (from the bridge) immediately sees the emitter has been activated.

So, according to this synopsis, the mobile emitter has to be attached to the left sleeve of the hologram.

From another episode (I forgot which), A character (B'Elanna?) was kneeling/squatting, attempting to activate the Doctor using the mobile emitter. When it was successful, the doctor materialized, the mobile emitter on his left sleeve. Since the mobile emitter was at a significantly lower height than the Doctor's left sleeve, the Doctor materialized in a crouching/kneeling/slouching position.

It seems the mobile emitter is hard-coded to be on the hologram's left sleeve.

Is there an instance where the mobile emitter was used on a non-humanoid, or in a location OTHER than the left sleeve?

  • I don't think your presumption is quite correct. Given the stated evidence, the only assumption we can really make is that the mobile emitter needs to be in physical contact with the subject hologram to work. We might also infer that a certain amount of surface contact with a certain face of the emitter, for a certain duration, is required to activate it. However, I take the holodeck character's preference of their left sleeve as merely coincidental - perhaps based on some presumption the holodeck character themselves is making about the emitter's operation, based on their own observation.
    – Iszi
    Sep 26, 2012 at 19:10
  • Perhaps. I guess we'll never know. Sep 26, 2012 at 20:31
  • The Doctor's emitter was on his ankle at least once, I belieeeve in Live Fast and Prosper, so the arm is probably just a default.
    – Izkata
    Sep 27, 2012 at 0:06
  • He wore it on his ankle while pretending to be Janeway at one point.
    – sevvack
    Mar 18, 2015 at 16:03
  • The episode was 'Renaissance Man', he wore the emitter on the ankle under the trouser leg, while imitating various people, I think Iszi is right physical contact is all thats needed (maybe the battery justs lasts longer in the 'default' sleeve position who knows or maybe he just does it because that was where it was put when he first got activated with it on)
    – Matt
    Sep 22, 2016 at 14:17

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