Posted By George Wedgwood Firstly, refer to the HSE Free leaflet on 'Reversing Vehicles' INDG 148. There are a number of potential problems associated with such alarms and environmental noise is just one of them. You should consider a range of other control measures as well and also try and select the type of alarm to suit the workplace - i.e. we have found the 'Brigade' ambient noise sensitive type to be very good, and it come in broadband noise type for less intrusion (see http://www.reverseinsafety.co.uk/press8.html). Also read the other HSE docs in their website for further info.(http://www.hse.gov.uk/pubns/tranindx.htm) Hope this helps, George