D&D 5E Would you require a roll for this?

[Andvari]

If you want to stock your dungeon or fortress with traps, get some help from the Kobolds. Trapmaking is their favorite profession. "This is Trapmakers R Us, how may we stock your dungeon?"

Also a great way to have weak monsters part of a dangerous dungeon. They might run when they see the PCs, and they might die in 1 hit. But the dungeon is still challenging because of their traps.

 

[ezo]

I think we’re mostly on the same page here.

I concur.

The only quibble would be with your qualifiers that “people can be clumsy” or ascribing “nerves” to PCs — bold adventurers are typically not clumsy and it’s up to the players to determine how their PCs think and act so, as DM, I’m not going to build those qualifiers in as reasons to call for rolls at our table.

PCs can certainly have DEX 8 or lower, being just as clumsy or graceful as "common folk". They might or might not have Athletics or Acrobatics or whatever. While I agree the majority have DEX 12 or better (IME), lacking an appropriate proficiency can have an impact, even on a very easy DC 5 with advantage.

PCs can also be frightened, and players can role-play their PC as they want of course, my point was simply that people do get nervous in dangerous situations, so a bad roll (failing the required check) could be due to nerves, or clumsiness, or whatever.

As both player and DM, either way is fine with me, and I can understand others taking either view.

 

[Hriston]

Poison Needle​

Mechanical trap​

​

A poisoned needle is hidden within a treasure chest's lock, or in something else that a creature might open. Opening the chest without the proper key causes the needle to spring out, delivering a dose of poison.​

When the trap is triggered, the needle extends 3 inches straight out from the lock. A creature within range takes 1 piercing damage and 11 (2d10) poison damage, and must succeed on a DC 15 Constitution saving throw or be poisoned for 1 hour.​

​

A successful DC 20 Intelligence (Investigation) check allows a character to deduce the trap's presence from alterations made to the lock to accommodate the needle. A successful DC 15 Dexterity check using thieves' tools disarms the trap, removing the needle from the lock. Unsuccessfully attempting to pick the lock triggers the trap.​

My comments here are with reference to the above quoted trap from the Basic Rules and the situation described in the OP. The way I'm reading this trap (which is badly written and self contradictory if I'm understanding it correctly), you have two chances to avoid the damage and subsequent saving throw. The first is by deducing the presence of the trap, which is what it seems the rogue in the OP was able to do. The text of the trap sets the DC for this at 20, success meaning the trap is revealed and damage avoided. The trap can be safely triggered as in the OP (although my personal preference for how this is accomplished would be more along the lines of the rogue’s player describing using an extra long tool from their set for this purpose rather than the gauntlet exploit described in the OP, but the details aren’t important as long as the fiction is acceptable to everyone at the table), and the lock can be picked without danger for which I wouldn’t ask for a check.

If the effort to investigate the lock fails, however, or the character doesn’t even bother to examine the lock before attempting to pick it, there's a second chance to avoid taking damage and saving against poison by picking the lock without triggering the trap -- the DC 15 check with thieves' tools. Success on this check means the lock picking attempt manages to emulate the use of the proper key closely enough that it disarms the trap. Failure would mean opening the chest and triggering the trap because the proper key wasn't used.

 

[Lakesidefantasy]

Sorry if this is out of place but I like to skip the discussion before I answer one of these kinds of questions so as not to be influenced by my peers.

I would call for a roll with disadvantage to pick the lock due to the bulky nature of the gauntlets. However, if there is no pressure to get this done quickly, I would not call for the roll because they're just going to keep trying until they succeed and the gauntlets will prevent the injection of poison.

My concern is they would just wear gauntlets all the time now. Fine, but they're going to be picking locks and finding traps at disadvantage. Maybe they'll only put on the gauntlets when they're dealing with chests. Fine, especially if a lot of chests are trapped with poison needles, but the gauntlets aren't going to save them from poison gas.

I mean, how often do they run into poison needles traps? If it's common then that's boring and maybe we should consider other kinds of traps. If it is rare then no problem because it's not likely that this exploit will undermine the game.