The Smart Port Brushles RPM and dual temperature sensor plugs it into a Smart Port equipped receiver (X series, will not work with D series receivers). Join the red and black wires to any 2 of the 3 wires going to your brushless motor, and you can now read the RPMs.
You will need to program the sensor to set correct the pole count of your motors.
This kit also includes two temperature sensors for you to monitor the temperature of the battery and ESC.
Specifications: