Dive Science - 2 divers diving in the ocean
Apnea Alerts

Apnea Alerts

In free diving, it can be challenging to track time, depth and speed during a dive, and every glance at the dive computer takes valuable seconds away from a dive that is limited by a single breath.

Apnea alerts are designed to convey information through audible and haptic feedback that provides situational awareness and reduces the need for a diver to look at their dive computer during a dive. This helps divers perfect their techniques and stay within their limits for safer and more efficient diving.

Depth Alarms

Depth-based alarms will alert a diver when they have reached a specific depth. Depth alerts can be set to a specific depth (i.e., 10 meters) or can be set to repeat at a specific interval (i.e., every 10 meters). Depth alerts can also be set to trigger when a diver reaches the target on a descent, on an ascent or both.

Special Depth Alarms

In addition to basic depth alarms for custom depth, interval and direction, there two additional types of depth alarms: neutral buoyancy and target depth.

Neutral Buoyancy Alert

The neutral buoyancy alert can be set to trigger on ascent or descent and should be set to the depth where a diver is neutrally buoyant in the water with their equipment.

A diver should test their neutral buoyancy depth setting at the beginning of every dive session and whenever they change equipment to ensure accuracy. You can edit, enable or disable neutral buoyancy alerts in the apnea alerts menu.

Set up from the dive menu:

  • When starting an Apnea or Apnea Hunt activity, press Up from the predive screen.
  • Select Apnea Alerts → Neutral Buoyancy.
  • Enable/disable, edit depth or direction.

While on the surface:

  • Before a dive, press Start/Stop to enter the surface menu.
  • Select Apnea Alerts → Neutral Buoyancy.
  • Enable/disable, edit depth or direction.
  • If changing equipment, always test your neutral buoyancy for accuracy.

Why is neutral buoyancy important?

A free diver's buoyancy changes during a dive. At the surface with a full breath of air, a diver should have positive buoyancy, meaning they are floating. This buoyancy is due to the volume of air in a diver's lungs as well as the buoyancy of the diver's exposure suit. A free diver will commonly wear a weight belt to offset some of this buoyancy, making it easier to dive below the surface.

As a diver goes deeper, their buoyancy is reduced due primarily to the compression of neoprene in their exposure suit and the air in their lungs. At a certain depth, the diver's buoyancy will switch from positive to neutral. This is the point where a diver at rest will remain at the same depth, neither floating nor sinking. Above this depth, a diver at rest will float back to the surface. Below this point — negative buoyancy — a diver will sink.

A diver can adjust their neutral buoyancy depth with their weight belt. While a shallower neutral buoyancy makes it easier to dive deeper, a deeper neutral buoyancy is considered safer because it is easier to return to the surface. Divers should set their neutral buoyancy according to their training and equipment. Formal free dive training is available through a number of agencies, including PADI, PFI, SSI and Molchanovs. Certification is highly recommended for anyone doing apnea dives.

Buoyancy Phases of Free Diving

  1. Surface to neutral buoyancy
    • At the beginning of a dive, a diver must work harder to overcome positive buoyancy.
  2. Neutral buoyancy to target depth
    • Below neutral buoyancy depth, a diver will be able to maintain the same descent rate with progressively less work and may eventually be able to go into freefall, where no kicking is needed to maintain a constant descent rate up to the target depth.
  3. Target depth to neutral buoyancy
    • After reaching a target depth and turning around, a diver must now overcome negative buoyancy to ascend toward the surface. This can be the most challenging part of a dive.
  4. Neutral buoyancy to surface
    • Once reaching neutral buoyancy on the ascent, a diver will be able to slow their kicking in order to maintain a safe ascent rate to the surface.

Target Depth Alert

The target depth alert can be easily changed during a surface interval and before each dive. It is meant to let a diver know when they have reached their maximum depth goal for an individual dive and will only trigger on the descent.

To enable/disable target depth alerts:

  • While on the surface, press Start/Stop to enter the surface menu.
  • Select Apnea Alerts, select Target Depth, then enable the alert by pressing Start/Stop.
  • This menu also allows you to change target depth and other alert settings.

To change target depth during a surface interval and before a dive:

  • Once target depth alerts are enabled, the depth can be quickly changed from the surface menu.
  • Before a dive, press Start/Stop to enter the surface menu.
  • Scroll to Target Depth, and enter the desired maximum depth of your next dive.
  • An alert will be triggered when you reach that depth on all subsequent dives until the target depth is changed or the target depth alert is disabled.

Time Alarms

Time-based alarms can be set to alert a diver of a certain time after the start of a dive or at a specific time interval. This can be helpful for a diver to keep track of the duration of their dive. A spear fisher or photographer, for example, may use the time alarms to keep track of time while their attention is focused on marine life.

Surface Timer

The surface timer provides an alert at a specified interval after the end of a dive. This can be used to help ensure a safe recovery interval between dives. The diver should set this time according to their training and the depth of their dive. The surface timer can be enabled and disabled from the predive checklist when starting an apnea session or through the apnea alerts menu.

Speed Alerts

In addition to time and depth alerts, Descent™ dive computers from Garmin can help a free diver maintain a target descent and ascent rate.


The dive variometer provides haptic and/or audible feedback to a diver that varies according to their vertical speed, also known as descent rate or ascent rate. The variometer provides feedback by pulsing and/or beeping at a specified depth interval. Every time a diver changes depth by that amount, the dive computer will pulse with a beep, vibration or both.

As a diver changes depth, the pulsing will increase or decrease in frequency according to the vertical speed of the diver. For instance, if a diver is descending at 1 meter/second with the default variometer depth setting of 1 meter/second, the watch will pulse every second. If the diver speeds up to 2 meters/second, the dive computer will pulse every half second. The tempo of pulsing can be used by a diver to understand their rate of ascent or descent.

Variometer Settings

  • Status: Enable or disable the variometer.
  • Depth: A smaller variometer depth setting will increase the frequency of pulses, while a larger variometer depth setting will reduce the frequency of pulses.
  • Direction: The variometer can be set to pulse while descending, ascending or both. The tone is different when descending versus ascending to help differentiate between the two.

High-speed and Low-speed Alarms

A diver can use the high-speed and low-speed alarms to know when their vertical speed is above or below a certain threshold. A low-speed alert could be used to help ensure the diver is kicking hard enough to maintain a certain speed, and a high-speed alert can help a diver know if they are going too quickly, which may be less efficient.