Touchless interaction devices

An electronic device comprising

• a front surface incorporating a display screen,
• a rear surface comprising one or more protruding portions which cause a recessed portion of the rear surface to be held away from contact with a flat supporting surface when the device is laid down,
• at least one ultrasonic transmitter and
• at least one ultrasonic receiver, wherein at least one of the ultrasonic transmitter and the ultrasonic receiver is disposed on the recessed portion of the rear surface of the device and is also held away from contact with said flat supporting surface, the device being configured to transmit signals from the transmitter and to receive said signals at the receiver after reflection from a user's hand and to use said reflected signals to detect one of a predetermined set of gestures carried out adjacent to the device when the device is placed on its rear surface on said flat supporting surface, wherein said signals from said transmitter are reflected from said supporting surface as well as from said user's hand before being received at said receiver.