Abstract: A contactless coded key system, comprising a key 2 and key terminal each housing circuitry enabling information to be transferred from terminal to key, and vice versa, and enabling the key to be powered from the terminal. This circuitry also comprises a light emitting diode and phototransister by means of which the presence of a key in the terminal is sensed. In a fuel monitoring application for a vehicle fleet, for example, each driver has a key enabling him to draw fuel from one or more depots each including a terminal. Fuel dispensed can be logged and fuel economy calculated.