The Tracker Listen Only Earpiece is exceptionally comfortable and durable. An earpiece is so important for safety by keeping you stealthy and not making your subjects aware of private communication. With the Tracker you can be sure you won't miss an important call! The Kevlar reinforced wire and stapled strain reliefs make it the perfect item to survive the rigors of police work. With the "Semi-Custom Skeleton" you have the perfect unit for 12-hour comfort and the security. The unit won't come out of your ear. The Tracker 42" is designed for use where you plug it directly into your radio or the "tower" of the shoulder mic.If you need to plug directly into the shoulder mic please choose the Tracker 12".