Why Do Back-Up Alarms Have To Be Noisy?

When they are working as intended, back-up alarms—in common with some forms of modern music—broadcast annoying sounds for several blocks. The I-405 Sepulveda Pass Improvements Project has been trying to do something about this.

The answer may rely on a duck or, at least, the sound of a duck.

Back-up alarms are annoying by design in hopes of reducing collisions between construction workers and the far larger vehicles surrounding them. These collisions are not a rare problem.

The United States Bureau of Labor Statistics states that six percent (397 deaths) of all fatalities in the construction industry in 2002 resulted from workers being struck by vehicles. Consequently, Cal OSHA requires back-up alarms for worker safety.


To reduce this loss of life, the high-pitched beeping of back-up alarms tries to convey urgency to nearby workers, to interrupt their thoughts and concentration. Unfortunately, the sounds from traditional narrow-band alarms can travel far outside construction zones, especially during the quiet hours of early morning.

Enter a recently developed technology and the ancient duck.

Kiewit Infrastructure West, prime contractor for the I-405 project, has addressed community complaints by fitting its construction vehicles with “broadband sound” back-up alarms. They sound similar to a quacking duck. (Sorry, bird watchers, no indication what species of duck is being mimicked.)

Because they broadcast over a broader band (400 to 10,000 megahertz) than the traditional narrow-band devices, the sounds from the new alarms should more tolerable.

They also bring another weapon to the fight against construction injuries. Workers hear the alarms as more localized, meaning it is easier for them to ascertain which vehicle has begun reversing.

Manufacturers tout an additional advantage to the new alarms. Apparently, humans require less volume to respond to the broadband alarms than to the traditional alarms, meaning the alarms will be quieter to those living near construction sites.

Because not all agencies and subcontractors have followed Kiewit’s example and fitted their vehicles with the new alarms, project neighbors may still hear the traditional alarm.

Yet, more change awaits. Alarm manufacturers have now developed speaking back-up alarms. They communicate with urgent phrases such as, “Stand well clear. Vehicle reversing.”