Purchase Decisive was the variable volume, as has been described in a review praising me. This I can only confirm - super !! Have been using the same batteries with Gong ordered, but I did not need. . If you are from a minimum 3-core cable Klingeltrafo for Gong and another 2-core cable to the bell, you can change with little effort the wiring so that no more batteries of distress are - kudos to the manufacturer !! Time installation with changing the wiring tidy and arrange tool was approximately 50 min.