The Kanohi Arthron was the Mask of Sonar. It allowed its wearer to locate beings or objects through echolocation. Toa Mahri Jaller wore this mask.1
Notes
The Kanohi Arthron was the Mask of Sonar.2, 3 It allowed Jaller to spot enemies even in the black waters around Mahri Nui.2
The Mask of Sonar allowed its user to locate other things in the water, but didn't identify if they were friend or foe.4
The Mask of Sonar bounced sound waves off objects.5
The Mask of Sonar couldn't detect disturbances in sound patterns.6
The Mask of Sonar showed its user that there were objects near them and whether they were moving or not, but didn't detect their identities.7
An Arthron user could likely sense a Volitak user.8
An Arthron user could see a Huna user.9