The Kanohi Arthron is the Mask of Sonar. It allows its' user to sense the movement and positions of targets through echolocation. The wearer can also use this mask to examine their surroundings in darkness. This mask is one of the few that can detect an invisible target, such as a Kanohi Huna-user. As with real sonar, it identifies the general shape and movement of its' target, but does not provide details. A Kanohi Arthron is always on at a low level.
- Toa Gielinor Narok - Primary mask.
- Toa Mahri Jaller - Primary mask.
- Toa Neţeru Nebt-het - Primary mask.
- Toa Ryhmä Bakovu - Formerly; now deceased.
- Warga Tenrah - Formerly; now deceased.
- Warga Zaathu - Formerly; now deceased.
- Kraahua - Formerly; now deceased.
- Nebt-het - Formerly; became Great when she was transformed into a Toa Neţeru.