Replacement Desiccant Blocks for Dry and Store - both Professional and Global models. Collect moisture that is drawn from hearing aids during drying cycle. One Dri Brik will last for two months. A visual Timestrip on the top of the block will let you know when it's time to replace it. Dri Briks will keep indefinitely if the package remains sealed. A package of 3 will give you six months of service.