Blow past a required decompression stop and every dive computer notices. What happens next is where the industry splits into two worldviews. Suunto grounds you: a serious violation triggers an error state that refuses deco calculations for about two days. Garmin benches you more briefly, timing out dive functions for roughly a day. Shearwater does something more radical — nothing punitive at all. It tells you what happened, flags the record, and keeps working. Three brands, three answers to one uncomfortable question: whose judgment runs the dive — the diver's or the manufacturer's?
What a Violation Actually Is
A required stop exists because the algorithm calculates that your slower tissues are holding more inert gas than a direct ascent can safely release. Surface anyway and the model's confidence in your tissue state collapses — you have exited the envelope the math was built to describe. Every brand agrees on that physics. The disagreement is purely about what the computer should do with a diver it can no longer model confidently.
The Suunto Position: The Surface Interval Is the Treatment
Suunto's roughly forty-eight-hour lockout encodes a straightforward safety claim: after a serious violation, the correct dive plan is no dive, and a grounded computer enforces the correct plan. There is real honesty in this — the physiology does not negotiate, off-gassing takes the time it takes, and a recreational diver tempted to rationalize a next-morning dive is exactly the person the lockout protects. Paired with the brand's conservative proprietary algorithm, it is a coherent philosophy: the computer is the adult in the room.
The cost of coherence: the computer cannot know context. The instructor with an emergency-assisted ascent, the diver whose stop was cut short by a genuine surface emergency, the remote-trip diver for whom the alternative to a working computer is diving tables from memory — all get the same grounding as the reckless case. Critics also note the perverse incentive: a locked-out diver who chooses to dive anyway now dives with no deco information, the worst possible outcome.
The Garmin Position: A Shorter Bench
Garmin's Descent line takes a middle road — dive-mode timeout on the order of a day after ignoring required deco. Same paternal instinct, smaller dose, calibrated to the recreational-to-light-technical audience the watches serve. It shares Suunto's logic and Suunto's blind spot to context, but the shorter bench means fewer scenarios where a traveling diver's trip is functionally ended by the watch.
The Shearwater Position: Information, Not Punishment
Shearwater's refusal to lock out is not permissiveness — it is a different theory of safety. The reasoning: a violation means the diver needs more accurate information, not less; the computer should display the degraded situation honestly, log it, and continue computing, because the diver who will dive again regardless is safer with a working instrument than a grounded one. It treats the diver as the responsible party and the computer as an instrument — the same philosophy behind the brand's open Bühlmann gradient-factor algorithm, where nothing is hidden and everything is adjustable. Technical divers, who train explicitly for contingency management, overwhelmingly prefer this stance; it is a core reason tool-style computers own that market, as our Perdix 3 guide explores.
The cost runs the other way: trust extended to every diver includes divers who have not earned it. A newly certified diver rationalizing a next-morning dive after a blown stop gets no guardrail from a Shearwater — only a flag in the log and the assumption that their training will speak up.
Three Philosophies at a Glance
| Suunto | Garmin | Shearwater | |
|---|---|---|---|
| After serious violation | Deco lockout, ~48 hours | Dive-mode timeout, ~24 hours | Flagged, keeps computing |
| Underlying claim | The interval is the treatment | Same, shorter dose | Information beats enforcement |
| Protects best | The diver who would rationalize | The recreational middle | The trained diver in a contingency |
| Fails worst | Context it cannot see | Context it cannot see | Judgment that is not there |
| Pairs with | Proprietary conservative model | Bühlmann-based implementation | Open Bühlmann GF |
Which Philosophy Should You Buy?
Match the computer's trust model to your honest self-assessment, not your aspirational one. New and occasional divers genuinely benefit from guardrails — the Suunto lane encodes the caution their experience has not yet built. Divers pursuing training, redundancy habits, and contingency planning grow into the Shearwater stance, where the instrument informs and the diver decides. And every diver, whatever the wrist says, answers a violated stop the same way: end the diving, watch for symptoms, and treat anything unusual as a DAN call rather than a debate with firmware. The best lockout policy is the one you never trigger.
Shearwater Perdix 3 $$$
The information-not-punishment flagship: open algorithm, no lockout, and the assumption that your training is real.
Suunto Nautic S $$
The guardrail philosophy in its friendliest 2026 form — conservative model, firm boundaries, rechargeable at last.
Verdict
Lockout policy is the rare spec that is really a mirror: it tells you what a manufacturer assumes about you. Suunto assumes you might need saving from yourself; Shearwater assumes you will not; Garmin hedges. All three are defensible — and none of them off-gasses a single tissue compartment. Pick the assumption that matches the diver you actually are today, and let your training, not your firmware, be the thing that keeps stops from getting blown at all.
Frequently Asked Questions
What is a dive computer lockout?
A lockout is a post-violation state where the computer refuses to provide decompression calculations for a set period, typically one to two days, after a diver seriously deviates from its required stops. The computer may still show depth and time but will not compute deco, effectively grounding algorithm-guided diving.
Does Shearwater ever lock you out?
No. Shearwater's stated philosophy is to display accurate information and trust the diver's training. After a violation it flags the event and keeps computing with degraded-confidence context, on the reasoning that a diver who must dive again is safer with a working computer than without one.
How long is a Suunto lockout?
Suunto's error state after a serious deco violation traditionally grounds deco calculations for roughly forty-eight hours, reflecting the physiological reality that violated tissues need surface time regardless of what any display says.
If I get locked out, is it safe to dive anyway?
The lockout exists because your recent profile carries elevated decompression-sickness risk, and the conservative answer is that the surface interval is the treatment. Any symptoms after a violated stop are a medical question for DAN or a dive physician, not a gear question.
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