Which device alerts firefighters when the air cylinder capacity reaches 25%?

The Vibralert is the correct choice because it is specifically designed to notify firefighters when the air cylinder capacity drops to a critical level, typically around 25%. This device provides a tactile alert through vibrations, ensuring that firefighters are made aware of their air supply status, which is crucial during emergency situations where every breath counts.

The Vibralert system enhances situational awareness by enabling firefighters to focus on their tasks without having to constantly monitor their air levels visually. This becomes especially important in environments where visibility may be compromised by smoke or other hazards.

Other devices may have different functions or alert thresholds. For instance, a dual alert system or sound signal device generally serve to provide alarms for various conditions but may not specifically target the air supply status at the 25% threshold. Similarly, a pressure monitor is used primarily to give ongoing readings of air pressure but doesn't specifically issue an alert at a defined capacity level, making the Vibralert the dedicated solution for this particular requirement in firefighting operations.