The product in question is called the safedraw. It attaches to you berger hole in replace of your rest. It then attaches the string, and by using pneumatics, it allows you to safely draw and release your bow without an arrow. It does not weigh too terribly much, and the cost is around $100. The member here by the name of BeeS has one one one of his bows, and it is a great aid for working on form, release, and back tension.