A radar detector enabling hands-free communication over a mobile phone by connecting the mobile phone to the radar detector. The radar detector includes a horn antenna; a signal-processing unit (SPU) for detecting a signal received by the horn antenna; a laser module for receiving a laser signal; a central processing unit (CPU) for controlling the SPU; a pulse delay unit for delaying or sustaining a CPU pulse; a sweep voltage generator unit for driving the SPU; a warning unit for warning the detected signal; an audio amplifier controller connected to the CPU and the warning unit to amplify an audio signal; and a connecting unit installed to connect the audio amplifier controller with a mobile phone. The connecting unit includes a microphone, a switch for reception of a signal from the mobile phone, and a connection portion for connection to the mobile phone.