What is the safety function of smoke detectors fitted in isolated coach compartments such as a toilet or luggage bay?

1. They monitor only temperature and cannot respond until open flame is present
2. They detect early smoke particles from illicit smoking or incipient fires in isolated compartments and trigger visual and acoustic alarms on the driver's dashboard
3. They automatically open exterior compartment doors while the vehicle is moving
4. They replace the driver's duty to stop, assess the alarm, and begin the emergency procedure