Researchers are studying whether artificial-intelligence tools that analyze things like typing speed, sleep patterns and speech can be used to help clinicians better identify patients with early-stage dementia. Huge quantities of data reflecting our ability to think and process information are now widely available, thanks to watches and phones that track movement and heart rate, as well as tablets, computers and virtual assistants such as Amazon Echo that can record the way we type, search the internet and pay bills.

There is a pressing need to automatically understand the state and progression of chronic neurological diseases such as dementia. The emergence of state-of-the-art sensing platforms offers unprecedented opportunities for indirect and automatic evaluation of disease state through the lens of behavioural monitoring. This paper specifically seeks to characterise behavioural signatures of mild cognitive impairment (MCI) and Alzheimer's disease (AD) in the \textit{early} stages of the disease. We introduce bespoke behavioural models and analyses of key symptoms and deploy these on a novel dataset of longitudinal sensor data from persons with MCI and AD. We present preliminary findings that show the relationship between levels of sleep quality and wandering can be subtly different between patients in the early stages of dementia and healthy cohabiting controls.