The warning indicator is mounted on the canister housing's outlet to the inhalation side. The warning indicator contains a spring loaded non-return valve the position of which is visible on the white pin. In operation, the warning indicator is pressurised from the dosage warning in the regulator block via the adjustable nozzle. This is visible from the white pin being pushed out and becoming visible. When the IS-MIX is depressurised or in warning position, the non-return valve is closed and the pin is retracted.

In the event of a warning, the flow from the dosage warning in the regulator block is throttled and the non-return valve then throttles the flow of gas and the diver is alerted to the warning of a possible fault.