In this paper we detail the design intricacies and implementation details of a novel Selective Activity Monitoring (SAM) system targeted for homes for the elderly. The system is designed to support people who wish to live alone but are at risk because of old age, ill health or disability. The system works on the principle of using sensor units (SU) to monitor the appliance throughout a house and detect when certain desired electrical equipments are turned on. Rules are defined for appliances to turn on in certain time intervals or turn off after a cut-off time. The rules are flexible and can be user-defined based on the daily activities of a person. Several levels of alarm conditions have been created based on combination of rules that are violated. Any number of sensor units may be installed in a house, one each to monitor an electrical appliance. A central controller unit (CCU) queries the sensor units and logs the data into a PC at a pre-defined rate. Communication between the SUs and the controller is using radio-frequency wireless media. The rules inference engine runs on the PC and whenever the situation warrants, sends a text message to the care-givers or relatives. Since no vision sensors (camera or infra-red) are used, the system is non-invasive, respects privacy and has found wide acceptance. The system is completely customizable, allowing the user to select which appliances to monitor and define exactly what is classified as unusual behavior.