The IV's were an improvement over the III's we had, but the II's are by far the best. Sometimes they activate, sometimes they don't.
My whole town is about 1.5 sq miles, with repeaters (yes, a little overkill) so we are not in a fringe/remote area. It's either too low or too loud, the ad silence. My volume control goes from off to about 1/3, then complete silence for 1/3, then loud for 1/3 of the range. Very helpful when checking to see which pagers activated for what calls and which didn't. They are programmed to playback the last 4 activations.
I have never personally used the vibrate mode, but others have said it's good. Some members only use 2 and have dispatch and fireground channel in their programming, others, like myself, have 2 additional.
