Portable collision avoidance system

A portable collision avoidance system (PCAS) is a proprietary aircraft collision avoidance system similar in function to traffic collision avoidance system (TCAS). TCAS is the industry standard for commercial collision avoidance systems but PCAS is gaining recognition as an effective means of collision avoidance for general aviation and is in use the world over by independent pilots in personally owned or rented light aircraft as well as by flight schools and flying clubs.

Source: Wikipedia — Portable collision avoidance system (CC BY-SA 4.0)