An autonomous device configured to move within a space, the autonomous device comprising: a first system to detect a first location of the autonomous device within the space, the first location being based on a first fixed landmark reference; a second system to detect a second location of the autonomous device within the space; a third system to detect a third location of the autonomous device within the space based on relative movements of the autonomous device; the autonomous device being characterised by: the second location being based on a second fixed reference that comprises a remote receiver (41, 42, 43), wherein the second system comprises a transmitter for transmitting signals; and a receiver for receiving timestamp messages based on the signals; and by the autonomous device comprising: one or more processing devices, wherein the one or more processing devices are configured to determine the second location based on a transmitted signal and a timestamp message corresponding to the transmitted signal, the timestamp message containing a time that the transmitted signal was received by the remote receiver, and to select one of the first location or the second location based on reliability of at least one of the first location or the second location, and to control movement of the autonomous device using an estimated location that is based on the third location and the selected one of the first location or the second location,. a first system to detect a first location of the autonomous device within the space, the first location being based on a first fixed landmark reference; a second system to detect a second location of the autonomous device within the space; a third system to detect a third location of the autonomous device within the space based on relative movements of the autonomous device; the autonomous device being characterised by: the second location being based on a second fixed reference that comprises a remote receiver (41, 42, 43), wherein the second system comprises a transmitter for transmitting signals; and a receiver for receiving timestamp messages based on the signals; and by the autonomous device comprising: one or more processing devices, wherein the one or more processing devices are configured to determine the second location based on a transmitted signal and a timestamp message corresponding to the transmitted signal, the timestamp message containing a time that the transmitted signal was received by the remote receiver, and to select one of the first location or the second location based on reliability of at least one of the first location or the second location, and to control movement of the autonomous device using an estimated location that is based on the third location and the selected one of the first location or the second location,. the second location being based on a second fixed reference that comprises a remote receiver (41, 42, 43), wherein the second system comprises a transmitter for transmitting signals; and a receiver for receiving timestamp messages based on the signals; and by the autonomous device comprising: a transmitter for transmitting signals; and a receiver for receiving timestamp messages based on the signals; and by the autonomous device comprising: one or more processing devices, wherein the one or more processing devices are configured to determine the second location based on a transmitted signal and a timestamp message corresponding to the transmitted signal, the timestamp message containing a time that the transmitted signal was received by the remote receiver, and to select one of the first location or the second location based on reliability of at least one of the first location or the second location, and to control movement of the autonomous device using an estimated location that is based on the third location and the selected one of the first location or the second location,. to determine the second location based on a transmitted signal and a timestamp message corresponding to the transmitted signal, the timestamp message containing a time that the transmitted signal was received by the remote receiver, and to select one of the first location or the second location based on reliability of at least one of the first location or the second location, and to control movement of the autonomous device using an estimated location that is based on the third location and the selected one of the first location or the second location,.