The simplest and most reliable attention getter for scuba diving is the Tank Banger from ISC. Just stretch it over the base of your scuba cylinder and your ready to go. If you're right handed place to the right if you're left handed place it to the left. You need to get someone's attention underwater just pull the ball away from you cylinder and let go BANG! Get the attention of your buddy, your students, or other divers from long or short distances. The ISC Tank Banger is made of corrosion free plastic and surgical rubber tubing.