For $10, this is a great testing box. However, it has a couple of annoyances:

1. The buzzer is *really* loud. I had to tape over the "speaker" (a small hole in the case) to make it tolerable.
2. There is no way to switch it off without unplugging the battery, and that is not easy. You have to pry off the back panel, and there is no good place to start; it's just one solid wall of plastic. It takes some effort to do.

Once you get around these issues, it works great. 4 stars