I tried to monitor them and did not get a peep or any type of audible signal and I was listenening fairly close. There are repeaters so proximaty should not be a problem. Several years ago I was talking to a jailer about the system and he said that it also keeps track of the prisoners. For example,if a prisoner has a visit the radio tracks him and he has so much time to get from point A to point B, if he doesnt make it in the allotted time an alert is sent out, So the radios must carry a lot of data/info also. According to FCC website the freqs used are a strange decimal points.The old jail used 452.9 and 453.