Most hearing aids will come with some sort of indicator so you can clearly see which one is for the right and left ear. A red mark typically indicates the right side, while blue marks the left. You can also figure out which side each hearing aid is designed for yourself. For behind-the-ear models, hold your device with the part that sits on top of the ear facing back. The earpiece should face forward. If the hearing aid you’re holding is designed for the right ear, then the earpiece will point to the left. If it’s for the left ear, the earpiece will point to the right. Once you’ve figured this out, you can use a permanent marker pen or drop of nail polish to mark out the left and right hearing aids. Make sure it fully dries before you place them back in your ear.