What usually triggers elevators to automatically go to the lobby in buildings?

Elevators are typically programmed to respond to a fire alarm to enhance the safety of all building occupants. When a fire alarm is activated, the elevators will often automatically return to the lobby to evacuate and prevent individuals from using them during an emergency. This standard procedure is designed to avoid the risk of getting trapped in the elevator, as fire and smoke can render others areas of the building unsafe.

While other scenarios, such as an intrusion alarm or smoke, may warrant a response, the fire alarm specifically triggers the elevator's emergency protocol to ensure that it reaches the safest level. In the case of a terrorist attack, building protocols may vary greatly depending on the nature of the threat, but they do not usually have a standard response associated with elevator operations like a fire alarm does.