Currently, Google has launched Android 9.0 system development, Android Open Source Project (AOSP), Android official submitted a new 'call recording' support, but when the call recording, the phone will be A tone of 1400 Hz, repeated every 15 seconds, is added to the call, and the sound will be heard by both parties on the call, allowing the other party to confirm that you are recording.
Due to the need to comply with regulatory requirements, Android native system may be added to this tone, but operators are free to choose whether to open or close the call recording tone is turned on.
Call recording function has emerged from the era of functional machine, third-party Android manufacturers have long been added in the call interface, the function, some third-party applications often call permission to confirm whether the call.
From now on to do this function, can only say that Google is making up the shortcomings of the native Android system.