Detect the robot

by Hemal
(Surat,Guj,India)

Robot Arena

I need to detect a incoming robot,and my robot will be moving in a circular path which is autonomous.

The circular path has wall of 10 cm height and slots provided at 60 degree offset.

There is flag at the center ...the radius of outer circle is 1230mm and inner circle is 600mm, the red line is in the middle.

When the incoming robot is detected.It has to give some kind of indication by a led or a buzzer,I don't know what sensors to use, don't know even their type,not even what microcontroller to use nor how to program it.

The other robot will try to capture the flag.