What indication will be present in the cab if a DER (door emergency release) is activated?

When a Door Emergency Release (DER) is activated, the cab will indicate this situation through a flashing door close light accompanied by a buzzer sound. This visual and auditory signal is critical as it alerts the operator that the emergency release has been triggered, which requires immediate attention to ensure the safety of passengers and proper operation of the train systems. The combination of the flashing light and buzzer is designed to be noticeable, minimizing the potential for oversight and prompting the necessary actions to address the situation.

In contrast, continuous horn sounds and steady lights would be indications of different alerts that do not specifically relate to the DER. All control lights turning off would not be a practical indication of a DER activation, as some signals need to remain active for safety alerts. Lastly, the door locking mechanism engaging would occur in normal operation rather than during an emergency release, making it an unlikely scenario linked to the DER activation.