This is the Futaba R2000SBM S-FHSS 2.4GHz S.Bus Port and RSSI Drone Racing Receiver.

 
Specifications: 
Size: 20x10x3mm (0.79 in x 0.39 in x 0.12 in) 
Weight: 2.9g (0.1 oz) 
Power Requirements: DC 3.7V~8.4V 
Battery F/S Voltage: 3.8V
 
NOTE: Be sure that when using ESC's regulated output, the current capacity of the ESC meets your usage conditions. The battery F/S voltage is set for a 4-cell NiCd/NiMH battery. Battery F/S function doesn't work properly when a different type of battery is used. The R2000SBM can be used with up to 8 channels. The fail safe function can be set for each channel. However, it differs according to the transmitter.