Durable for hard and intense use, and water resistant to sweat and rain, NoiZfree is a lightweight silhouette for telecoil (t-coil) hearing aid users. To enjoy crystal clear sound and noise-free use of cellphones, intercoms and audio sources (mp3 players, CD players, HiFi, etc.), simply switch the hearing aid to the T function (or MT in some devices) and place the earhook behind the ear. Includes a 2.5mm plug and a 3.5mm plug adapter. Auto shutoff.