I have built several of these, all work well and fantastic value for money.

Bought another one and mounted it in a waterproof box, with a 9,6V NiMh battery.

Moved the bluetooth board and adapter so that it would fit in the case, and also placed the bluetooth antenna on the outer edge of the box.

 

 

 

Hanging on the end of a long wire

 

 

 

 

And the trace on an Android phone