It is possible for a humidifier to trigger a Nest smoke alarm if it produces excessive moisture or steam that triggers the smoke detection sensors. The moisture can interfere with the sensors and cause a false alarm. To avoid this, it's best to place the humidifier away from the smoke alarm and ensure proper ventilation in the room. Additionally, choosing a humidifier with a built-in humidity sensor and automatic shut-off feature can help prevent excessive moisture buildup and reduce the risk of false alarms.