Q: Dear Sage,
Can a character use Disable Device to sabotage non-mechanical items? For instance, could he rig armor so that straps break the next time the wearer is hit, or a bowstring so it snaps the next time the bow is drawn?
A: The Disable Device skill specifically states that it applies to a “fairly simple or fairly small mechanical device” which suggests that non-mechanical devices are beyond its reach. You can’t sabotage a piece of parchment, or a shirt, or a pane of glass—you can only break them.
That said, the two items you describe are most certainly “mechanical devices”—most suits of armor include buckles, clasps, and the like (comparable to locks), while a bow is expressly designed to convert potential energy into kinetic energy (perhaps the very definition of a simple mechanical device).
Ultimately, the Sage thinks it’d be fair to use Disable Device to sabotage pretty much any item with moving parts. Treat them as either simple or tricky devices, determined by comparison to the examples given in the Disable Device skill.
However, you couldn’t time the failure as precisely as you describe in your question. The Disable Device skill suggests that you could rig such items to fail after 1d4 rounds or minutes of use, so it’d be up to the DM to determine exactly when failure occurs.
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