An extension unit for a keyboard, comprising: - a housing; - a button and/or key held by the housing; - an electronic module accommodated inside the housing to convert engagement with a button or key into coded form and to transmit the coded form to the electronic module of the keyboard for further transmittal to the computing device as user input, wherein the extension unit is configured to releasably attach the housing of the extension unit to a housing of the keyboard at a plurality of different locations, wherein the extension unit includes a left side and a right side opposite the left side, wherein the extension unit is configured to allow attachment of the left side of the extension unit to a right side of the keyboard and to allow attachment of the right side of the extension unit to a left side of the keyboard, wherein the extension unit includes an attachment device at the right side of the extension unit and an attachment device at the left side of the extension unit, characterized in that each attachment device (210, 211) is moveable between an operational position in which the extension unit can be attached to the keyboard using the attachment device and a retracted position in which the attachment device is prevented from engaging with the keyboard, and in that the attachment device at the right side is coupled to the attachment device at the left side so that an operational position of the attachment device at the right side corresponds to the retracted position of the attachment device at the left side and the operational position of the attachment device at the left side corresponds to the retracted position of the attachment device at the right side. - a housing; - a button and/or key held by the housing; - an electronic module accommodated inside the housing to convert engagement with a button or key into coded form and to transmit the coded form to the electronic module of the keyboard for further transmittal to the computing device as user input, wherein the extension unit is configured to releasably attach the housing of the extension unit to a housing of the keyboard at a plurality of different locations, wherein the extension unit includes a left side and a right side opposite the left side, wherein the extension unit is configured to allow attachment of the left side of the extension unit to a right side of the keyboard and to allow attachment of the right side of the extension unit to a left side of the keyboard, wherein the extension unit includes an attachment device at the right side of the extension unit and an attachment device at the left side of the extension unit, characterized in that each attachment device (210, 211) is moveable between an operational position in which the extension unit can be attached to the keyboard using the attachment device and a retracted position in which the attachment device is prevented from engaging with the keyboard, and in that the attachment device at the right side is coupled to the attachment device at the left side so that an operational position of the attachment device at the right side corresponds to the retracted position of the attachment device at the left side and the operational position of the attachment device at the left side corresponds to the retracted position of the attachment device at the right side.