Lifestyle monitoring (LM) technology is part of a new generation of telecare which aims to observe the daily activities of older or vulnerable individuals and determine if a medical or care intervention would be beneficial. The development and validation of new LM systems should ideally involve extensive trials with users in real conditions. Unfortunately, effective user trials are very challenging, generally limited in scope and costly. In this paper, a simulator is proposed that can serve to generate synthetic data of daily activity which can then be used as a tool for the validation and development of LM systems. The most challenging part of the simulator is to replicate people′s behaviour. In the paper, a novel model of daily activity simulation is proposed. Such daily activities are dependent on a number of external factors that control the need or desire to perform the activity. The proposed simulator aims to reproduce behaviour such that the probability of performing an activity increases until the need is fulfilled. It is possible to parameterise the behavioural model according to a set of features representing a particular individual. The simulator parameters have been populated using real world experiments through hardware testing and data collection with older people. Experimental verification that the desired features are reasonably reproduced by the simulator is provided.