... receiver and high penatrating detecting metal receiver and high-quality earphone, bringing out the best hidden listening effects.Unique FM ... : -70db Maximum Audio Magnification: 20, 000 times Listening Ways: Earphone, records, wireless FM transmitting Penetrability: Cement wall, Steel wall, ... iron wall, glass and air brick Usage: Put the earplug into headphone hole, the sonde into the MIC hole, and ...