There are two categories of sensors for healthcare application. The first category is called ambient sensors. Ambient sensor is used to monitor the general activity patterns based on spatial and temporal information processing. Examples of ambient sensors are fall detectors, door monitors, bed alerts, pressure mats, smoke and heat alarms etc. More recent works on ambient sensors involves camera, lighting, gas and humidity sensors. While these sensors can provide the surrounding activities, they cannot provide information concerning specific users. In this regard, wearable sensors can provide more detailed and user-specific information. These type of sensors often form a body sensor network (BSN) and combining BSN with ambient sensor provide a platform to establish a monitoring system which can offer rich contextual information .
 Feng Zhou; Jianxin Jiao; Songlin Chen; Daqing Zhang, “A Case-Driven Ambient Intelligence System for Elderly in-Home Assistance Applications,” Systems, Man, and Cybernetics, Part C: Applications and Reviews, IEEE Transactions on , vol.41, no.2, pp.179,189, March 2011