<p>There is described a signalling system operable to transmit data to a moving vehicle. The signalling system includes a first signalling device which is movable relative to a second signalling device by virtue of the first signalling device being mounted to a movable vehicle. One of the first and second signalling devices comprises a light source, a lens system for directing a light beam emitted by the light source in an exit direction within a field of view of the lens system, a detector for detecting the presence of the other signalling device, and means for varying the exit direction to align the optical beam with said other signalling device. By including the varying means, a low divergence light beam can be used which advantageously reduces the total power requirements. There is also described a financial transaction system in which low divergence free-space light beam is used to convey financial data. By using a low divergence light beam it is difficult for an eavesdropper to intercept the financial data.</p>
