The current health-care infrastructure is generally considered to be inadequate to meet the needs of an increasingly older population. We have investigated the feasibility of a passive in-home monitoring system based on wireless accessible sensor populations (WASP). In an EU-funded project we have identified the system architecture and the sensors required to gather data from elderly patients by continuous monitoring. Data from biological variables (heart rate, accelerometers, body temperature and galvanic skin response) and everyday habits (body position, movements) will be transmitted to a central monitoring centre. A Body Sensor Network (worn by the patient and able to communicate with a personal mobile hub) and an Ambient Sensor Network (a number of wireless sensors incorporated into the patient's home) are envisaged. The system will be tested by using it in the telemedicine activities of the Health Telematic Network, which manages home help projects for elderly patients.