In limiting the rapid spread of highly infectious diseases like Covid-19 means to immediately identify individuals who had been in contact with a newly diagnosed infected person have proven to be important. Such potential victims can go into quarantine until tested thus constraining further spread. This note describes a concept of mobile device (e.g. Smart phones) based approach for tracking interpersonal contacts which might have led to infection and alerting the potential victims. The approach assures means for defense against malicious usage while assuring a high level of privacy for all people involved.