Hobbywing Brushless Motor RPM Sensor
Specification:

Only work with Hobbywing High-Voltage version ESCs
Size: 23mm(L)*10mm(w)*2mm(H)
Weight: 6g (Input and output wires are included)
Working voltage: 3.5V to 8.4V(1S to 2S Lipo)
Current: 1 to 5mA Voltage range of the motor wires: 2 to 14S Lipo
RPM range (for 2 poles brushless motor): 1000rpm to 300000rpm.
Working temperature: 0 to 50 Celsius degree or 32 to 122 Fahrenheit degree