A security system having security devices with hierarchical levels of access provided to coded keys which may be hand held transmitter units, is disclosed. The levels of access are master which is restricted to the manufacturer, seller and installer, supervisor which can be allocated to a site, and user which is usually specific to one security device only. The security devices can be programmed to be responsive to all of the supervisor coded keys and/or user coded keys, or a user coded key only. The security system can be used in a method of securing all vehicles at a car sales, where all of the vehicles can have their security devices programmed to be responsive to supervisor coded keys specific to the car sales site. When a vehicle is sold, its security device can be reprogrammed to be responsive to specific user coded keys only.