The default Dry Fire sensitivity setting should be a good starting point for most Shot Timers in most environments. However, there are several reasons why it may not be the right setting for your situation. First, it's possible for a Shot Timer to interpret ambient noise as shots fired. This is a function of both the specific microphone circuit in your Shot Timer, as well as volume of your ambient noise. Not every Shot Timer will "hear" sounds exactly the same, particularly in the low volume range for dry fire. As such, any 2 units will likely have different sensitivity values which start triggering on just ambient noise. This is normal. If your Shot Timer is triggering on ambient noise, simply increase the sensitivity setting in the Sensitivity sub menu until ambient noise no longer triggers shots. Second, it's possible that the sound of dry fire is too quiet for the standard setting to pick up. In this situation, the sensitivity can be reduced in the Sensitivity sub menu until the shots are triggered. It is also helpful to position the Shot Timer as close as is practical to the gun.