An exemplary monitoring device includes: a time chip connected to a connector to generate a time signal and a count signal when the connector is working, the time signal indicating how long the connector is in use, the count signal indicating that the total number of times the connector has been used should be incremented by one; a processor connected to the time chip to receive the time signal and count signal, and generate a data signal including a total service time and a total number of times the connector has been used; a clock generator connected to the processor to provide a clock signal; and an output port connected to the processor to output the data signal. The monitoring device keeps a watch on a connector for showing the service information about the connector to make an operator know if the connector needs to be replaced.