A method of providing a gesture-based user interface to an electronic device (2; 30; 112) by recognising a movement of an object as one of a set of one or more possible predetermined movements, the method comprising: continuously or repeatedly transmitting signals between at least two transmitter-receiver pairs (8-10, 8-12; 36a-38a, 36b-38b, 36c-38c, 40a-42a, 40b-42b, 40c-42c; 120-124, 120-126, 122-126, 122-128), said signals being reflected from said object to produce reflected signals; determining, for a first one of said transmitter-receiver pairs, whether a said reflected signal meets a first predetermined proximity criterion comprising at least one of (i) a maximum time of flight of the signal from the transmitter (8; 36a, 36b, 36c, 40a, 40b, 40c; 120, 122) to the receiver (10, 12, 38a, 38b, 38c, 42a, 42b, 42c; 124, 126, 128) via the object, and (ii) a minimum energy reflected from the object; storing first event data in an electronic memory when said reflected signal meets the first predetermined proximity criterion for the first transmitter-receiver pair; determining, for a second one of said transmitter-receiver pairs, whether, after the first event, a subsequent reflected signal meets the first or a second predetermined proximity criterion comprising at least one of (i) a maximum time of flight of the signal from the transmitter (8; 36a, 36b, 36c, 40a, 40b, 40c; 120, 122) to the receiver (10, 12, 38a, 38b, 38c, 42a, 42b, 42c; 124, 126, 128) via the object, and (ii) a minimum energy reflected from the object; and storing second event data in the electronic memory when said subsequent reflected signal meets the first or second predetermined proximity criterion for the second transmitter-receiver pair; accessing the first event data and second event data from the electronic memory; determining whether the first event occurred before the second event; and when the first event occurred before the second event, identifying the movement of the object as being one of said set of movements. continuously or repeatedly transmitting signals between at least two transmitter-receiver pairs (8-10, 8-12; 36a-38a, 36b-38b, 36c-38c, 40a-42a, 40b-42b, 40c-42c; 120-124, 120-126, 122-126, 122-128), said signals being reflected from said object to produce reflected signals; determining, for a first one of said transmitter-receiver pairs, whether a said reflected signal meets a first predetermined proximity criterion comprising at least one of (i) a maximum time of flight of the signal from the transmitter (8; 36a, 36b, 36c, 40a, 40b, 40c; 120, 122) to the receiver (10, 12, 38a, 38b, 38c, 42a, 42b, 42c; 124, 126, 128) via the object, and (ii) a minimum energy reflected from the object; storing first event data in an electronic memory when said reflected signal meets the first predetermined proximity criterion for the first transmitter-receiver pair; determining, for a second one of said transmitter-receiver pairs, whether, after the first event, a subsequent reflected signal meets the first or a second predetermined proximity criterion comprising at least one of (i) a maximum time of flight of the signal from the transmitter (8; 36a, 36b, 36c, 40a, 40b, 40c; 120, 122) to the receiver (10, 12, 38a, 38b, 38c, 42a, 42b, 42c; 124, 126, 128) via the object, and (ii) a minimum energy reflected from the object; and storing second event data in the electronic memory when said subsequent reflected signal meets the first or second predetermined proximity criterion for the second transmitter-receiver pair; accessing the first event data and second event data from the electronic memory; determining whether the first event occurred before the second event; and when the first event occurred before the second event, identifying the movement of the object as being one of said set of movements.