What exactly is the trigger for Iron Man's weapons?

[Adam Reynolds]

How exactly do the suits know when to fire the repulsors or other mounted weapons? Is it a Jarvis/Friday thing or is it a biomechanics thing based on the way he is holding his hands?

[Lord Revan]

How exactly do the suits know when to fire the repulsors or other mounted weapons? Is it a Jarvis/Friday thing or is it a biomechanics thing based on the way he is holding his hands?

It could be activated by the HUD the Iron Man suits have (at least in the MCU)

[Bedlam]

The HUD is only a display (by definition) the system could be tracking his eye movement and fires based on that and other facial movements but then you'd have to be careful if you sneezed.

[Adam Reynolds]

I was just checking, and in Iron Man 1 he uses the arm weapon without a helmet during testing, so it can't be the HUD at least in that scene. In Iron Man 3 he also fights and flies without the helmet, so it would have to be movement based in both cases. Though frankly I'm not sure how given that sometimes he moves in ways that don't seem like they would be a clear activation symbol

Though the precise targeted guns from Iron Man 1 are clearly HUD based as we see the system indicate targets before they fire. Flares are clearly verbally activated both times he uses them in that film as well, so it seems to be a mix of different things depending on the system. A few times we also just don't see inside the suit and he could very well be giving voice commands that we just don't hear.

[Solauren]

Knowing Tony Stark's habits from the comics and movies, he probably had multiple built in firing methods.

i.e "If repulsor is held up, but no preasure on a back plate, begin impressive looking and sounding power up. If preasure is applied to the plate, fire repulsor for 2 second burst. If preasure is held on the plate, continuous firing. If flight mode is engaged...."

[Gandalf]

At the time of Iron Man 3, didn't he have a neural interface? So that could explain functions as the suits get way more complex.

[Formless]

Perhaps there are toe activated buttons in the suit's boots? I know a lot of actual arm prosthetics take advantage of the feet to activate various functions imperceptibly to most people who wouldn't think to look down.

[Tribble]

In addition to what others have said IIRC In Civil War he uses a one-handed sonic weapon / low power repulsor while fighting Winter Soldier and clenches his hand when firing.

May not be indicative of his other weapons for the full suit but it seems likely there is some kind of hand / wrist / arm movement involved.

[Batman]

Definite neural control in IM3-the damned Mk42 reacted to his 'nightmares'. Also possible tactile control in the boots/gloves. When wearing heavy boots/gloves you can usually wiggle your fingers/toes around some without your hands/feet actually moving, the suits may use that for triggering functions