A diagnostic device for assessing one or more pre-clinical signs and/or symptoms of Alzheimer's disease in a subject, the device comprising: at least one processor; one or more sensors associated with the device; and memory storing computer-readable instructions that, when executed by the at least one processor, cause the device to: receive a plurality of first sensor data via the one or more sensors associated with the device; extract, from the received first sensor data, a first plurality of features associated with the one or more symptoms of Alzheimer's disease in the subject; and determine a first assessment of the one or more symptoms of Alzheimer's disease based on the extracted first plurality of features. prompt the subject to perform one or more diagnostic tasks; in response to the subject performing the one or more diagnostic tasks, receive a plurality of second sensor data via the one or more sensors associated with the device; extract, from the received second sensor data, a second plurality of features associated with the one or more symptoms of Alzheimer's disease; and determine a second assessment of the one or more symptoms of Alzheimer's disease based on the extracted second plurality of features, characterised in that prompting the subject to perform the one or more diagnostic tasks includes prompting the subject to transcribe one or more pre-specified sentences comprising special characters. at least one processor; one or more sensors associated with the device; and memory storing computer-readable instructions that, when executed by the at least one processor, cause the device to: receive a plurality of first sensor data via the one or more sensors associated with the device; extract, from the received first sensor data, a first plurality of features associated with the one or more symptoms of Alzheimer's disease in the subject; and determine a first assessment of the one or more symptoms of Alzheimer's disease based on the extracted first plurality of features. prompt the subject to perform one or more diagnostic tasks; in response to the subject performing the one or more diagnostic tasks, receive a plurality of second sensor data via the one or more sensors associated with the device; extract, from the received second sensor data, a second plurality of features associated with the one or more symptoms of Alzheimer's disease; and determine a second assessment of the one or more symptoms of Alzheimer's disease based on the extracted second plurality of features, characterised in that prompting the subject to perform the one or more diagnostic tasks includes prompting the subject to transcribe one or more pre-specified sentences comprising special characters. receive a plurality of first sensor data via the one or more sensors associated with the device; extract, from the received first sensor data, a first plurality of features associated with the one or more symptoms of Alzheimer's disease in the subject; and determine a first assessment of the one or more symptoms of Alzheimer's disease based on the extracted first plurality of features. prompt the subject to perform one or more diagnostic tasks; in response to the subject performing the one or more diagnostic tasks, receive a plurality of second sensor data via the one or more sensors associated with the device; extract, from the received second sensor data, a second plurality of features associated with the one or more symptoms of Alzheimer's disease; and determine a second assessment of the one or more symptoms of Alzheimer's disease based on the extracted second plurality of features, characterised in that prompting the subject to perform the one or more diagnostic tasks includes prompting the subject to transcribe one or more pre-specified sentences comprising special characters.