... echo interfere.8.Pinhole style, Widely used in jail room, interrogation room, visiting room.9.Restraining high intensity voice automatically, protecting rear ... -25~75°C14.Pinhole style, Widely used in jail room, interrogation room, visiting room.15.According with CE standard.Parameter:Monitoring Range 10 ... 100gStandard CE J. TRADIO mini head,hidden,prison/Jail room audio surveillance microphone