Back-up beeper

A back-up beeper, also known as back-up alarm or vehicle motion alarm, is a device intended to warn passers-by of a vehicle moving in reverse. Some models produce pure tone beeps at about 1000 Hz and 97-112 decibels. The back-up beeper was invented by Matsusaburo Yamaguchi of Yamaguchi Electric Company in Japan. It was first manufactured as model BA1 in 1963. ISO 6165 describes "audible travel alarms", and ISO 9533 describes how to measure the performance of the alarms.
Criticism.
Back-up beepers have been criticized by the public and in scientific literature. Beepers are at or near the top of lists of complaints to government road builders about road construction noise. There is published concern that due to desensitization and the cry wolf effect people tend to disregard ever-present alarm sounds, diminishing their effectiveness. The normal level of 1000 Hz pure tone beeps at 97-112 decibels, considerably higher than the long-term hearing loss limit of 70 decibels.
Brains do not adapt to the repetitive and persistent sound of back-up beepers, but have evolved to process natural sounds that dissipate. The sound is perceived as irritating or painful, which breaks concentration.
In some countries, back-up warning systems using blasts of white noise have become more common. White noise is more audible than monotone beeping over background noise, and one can more easily ascertain the distance and direction of the sound.
Regulations in the United States.
Back-up beepers or an observer are required by OSHA for earth-moving vehicles with an obstructed view to the rear and no one on the ground to help guide the driver. OSHA regulation 29 CFR Part 1926.601(b)(4) requires "a reverse signal alarm audible above surrounding noise level", but only when the motor vehicle has "an obstructed view to the rear". The determination of the noise level is left to the employer.
NHTSA requires electric vehicle warning sounds to alert pedestrians in electric and hybrid vehicles manufactured after 2018, for both forward and reverse travel at low speeds.