A method performed by one or more computing devices, the method comprising: receiving, from a radar receiver arranged to detect hand movement made in three dimensions by a driver of a vehicle while hands of the driver remain in contact with, or in proximity to, a steering wheel in an interior of the vehicle, movement data indicative of a hand movement made in three dimensions by the driver of the vehicle; determining that the hand movement indicated in the movement data from the radar receiver corresponds to an initial gesture of the driver of the vehicle; determining, based on the movement data from the radar receiver, that the initial gesture represents a particular gesture from among a first predetermined set of gestures for selecting an operating mode of a computing device, wherein the determining that the initial gesture represents a particular gesture from among a first predetermined set of gestures comprises: processing input representing features of the movement data with multiple machine learning classifiers (144a, 144b, 144c) that operate concurrently, each of the multiple machine learning classifiers being configured to recognize initial gestures in a different predetermined set of gestures; accessing context data indicating a current operating mode of the computing device; selecting one of the multiple machine learning classifiers based on the context data; and determining that the initial gesture represents the particular gesture based on output from the selected machine learning classifier; and in response to determining that the initial gesture represents the particular gesture: causing the computing device to enter an operating mode corresponding to the particular gesture; and determining, based on additional data from the radar receiver, whether subsequent hand movement of the driver represents a subsequent gesture from a second predetermined set of gestures that is different from the first predetermined set of gestures. receiving, from a radar receiver arranged to detect hand movement made in three dimensions by a driver of a vehicle while hands of the driver remain in contact with, or in proximity to, a steering wheel in an interior of the vehicle, movement data indicative of a hand movement made in three dimensions by the driver of the vehicle; determining that the hand movement indicated in the movement data from the radar receiver corresponds to an initial gesture of the driver of the vehicle; determining, based on the movement data from the radar receiver, that the initial gesture represents a particular gesture from among a first predetermined set of gestures for selecting an operating mode of a computing device, wherein the determining that the initial gesture represents a particular gesture from among a first predetermined set of gestures comprises: processing input representing features of the movement data with multiple machine learning classifiers (144a, 144b, 144c) that operate concurrently, each of the multiple machine learning classifiers being configured to recognize initial gestures in a different predetermined set of gestures; accessing context data indicating a current operating mode of the computing device; selecting one of the multiple machine learning classifiers based on the context data; and determining that the initial gesture represents the particular gesture based on output from the selected machine learning classifier; and processing input representing features of the movement data with multiple machine learning classifiers (144a, 144b, 144c) that operate concurrently, each of the multiple machine learning classifiers being configured to recognize initial gestures in a different predetermined set of gestures; accessing context data indicating a current operating mode of the computing device; selecting one of the multiple machine learning classifiers based on the context data; and determining that the initial gesture represents the particular gesture based on output from the selected machine learning classifier; and in response to determining that the initial gesture represents the particular gesture: causing the computing device to enter an operating mode corresponding to the particular gesture; and determining, based on additional data from the radar receiver, whether subsequent hand movement of the driver represents a subsequent gesture from a second predetermined set of gestures that is different from the first predetermined set of gestures. causing the computing device to enter an operating mode corresponding to the particular gesture; and determining, based on additional data from the radar receiver, whether subsequent hand movement of the driver represents a subsequent gesture from a second predetermined set of gestures that is different from the first predetermined set of gestures.