*A02(main unit 2pcs/set) has already paired (factory default setting) , You don't need to do the paring process.
*A01M (master unit and 3 unit A01) Paring process.
A02 (main unit 2pcs/set) paring process.
*Master unit (A01M) is not able to pair with a mobile phone, but it can pair with 3 another standard devices which you can talk 4 people at the same time. 
*The communication distance is 1.6km, but intercall out distance will be about 500m.
If you are 1km a way from your student, you cannot start intercall,
the student must come back to 500m close to you and connect, then the student can go far away.
How to record the rider's voice. At the same time,it improves the work efficiency of the video/photo shoot