Your dive computer communicates through alarms — audible beeps and visual warnings that tell you something needs your attention. Understanding what each alarm means before you hear it underwater is critical, because an alarm you don't recognize can cause confusion and poor decision-making at depth.
Ascent Rate Alarm
The most common alarm. Your computer monitors your ascent speed (typically 30 feet per minute or 9 meters per minute) and warns you if you're ascending too fast. Rapid ascents increase the risk of decompression sickness because dissolved gas doesn't have time to be eliminated through normal breathing. If this alarm fires, stop ascending, hold your depth, and resume at a slower pace.
NDL Warning
Fires when your remaining no-decompression time drops below a threshold (usually 2–5 minutes, depending on the computer). This is your signal to begin ascending now if you want to avoid mandatory decompression stops. Not an emergency — but ignoring it turns a recreational dive into a decompression dive.
Decompression Violation
The most serious alarm. Fires when you've exceeded your no-decompression limit and are ascending without completing required decompression stops. This means you have an obligation to stop at a specific depth and breathe off accumulated nitrogen. Ignoring a deco violation significantly increases DCS risk. If this alarm fires, stop, descend to the indicated stop depth, and follow the computer's instructions.
Maximum Depth Alarm
A user-configurable alarm that beeps when you exceed a depth you've set as your personal limit. Useful for staying within certification limits (60 feet for Open Water, 100 feet for Advanced Open Water, 130 feet for Deep Diver) or for dive plan adherence.
Battery & System Alarms
Low battery warnings typically appear on the screen as an icon or message, sometimes accompanied by a beep. A battery warning before a dive means: replace or charge the battery before diving. A battery warning during a dive means: the computer may shut down. Begin a controlled, conservative ascent immediately, including a safety stop.
Air Integration Alarms
Computers with wireless air transmitters add two more alarms: low tank pressure (typically at 700–1,000 psi) and critical tank pressure (usually 500 psi). The low warning means start thinking about ending the dive. The critical warning means ascend now — you're running out of breathing gas.