Wis. Stat. § 347.435: Vehicle monitoring and feedback.

Notwithstanding s. 346.88, a person may operate a vehicle that has a device mounted to the front windshield if all of the following apply:

(1) The device is designed to monitor the vehicle and provide feedback to the operator for the purpose of safety or improving vehicle operation.

(2) The device is mounted directly above, behind, or below the mirror required in s. 347.40 (1) or, if no mirror is present, at the location where the mirror would typically be mounted.

(3) The device is mounted in a manner consistent with applicable federal requirements if the vehicle is a commercial motor vehicle as defined in 49 CFR 390.5.