These may include falls, as well as environmental changes in the home such as floods, fire and gas leaks. Carers of people with dementia may be alerted if the person leaves the house or other defined area. When a sensor is activated it sends a radio signal to a central unit in the user's home, which then automatically calls a 24-hour monitoring centre where trained operators can take appropriate action, whether it be contacting a local key holder, doctor or the emergency services.