A lot of commenters seem to be a tad critical about the white noise type of reversing alarm, this shows just how blissfully ignorant they are. All workers on the site must have a Site Induction before starting work, part of the induction will include all the different types of alarms used on that site and therefore all workers should be aware of the white noise reversing alarm. If you have only ever worked in the soft environments of an office, call cantre, retail store, or other such environments, you wouldn't know this. If you have got some guts about you and have worked on construction sites you'd know that there are many other ways to get injured at work.