So I made an app that will help you out with dry fire. It is very simple, and currently only works on Android. It gives you the ability to set a start beep after a certain amount of time. You can also have it randomly start between 2-4 seconds. Then you set how long you want until the second beep. This is solely to help you out with dry fire.
There are other apps out there that will do this, but all of them seem weird or kludgey. Some also want you to pay them, or want additional permissions that I don't understand the rationale for. Mine is FREE. It will stay free.
Right now it isn't in the app store, because I need testers. If you'd like to test it out, ALSO FOR FREE, email me: info@graydogllc.com