Light aircraft are commonly fitted with key-operated doors (cabin, cargo compartments) and key-operated switches (magneto/starter) in a manner very similar to most road vehicles. Airliners are not fitted with any such key-operated door latches or essential switches. The difference is due to the security environments in which they are operated/stored. A light aircraft such as a Cessna 172 might be parked in an unmonitored location readily accessible to almost anyone. Airliners are practically never left unattended and unmonitored. But what happens when an airliner is sold out of commercial service and refitted as a private jet? Would such an aircraft still be attended or monitored full time? Do they get fitted with security devices such as key locks on the doors and/or some sort of key operated interlock to deter unauthorized entry or engine starts?