© 2019 European Society of Anaesthesiology. All rights reserved. BACKGROUNDThe effects of noise are harmful to patients in the ICU environment, and the latter are particularly noisy places. High noise levels seem to be a factor in sleep disturbance, which can, in turn, result in increased morbidity.LOCAL PROBLEMHigh noise levels are a recognised problem in ICUs worldwide.OBJECTIVE(S)The goal was to estimate the effect of a visual noise-warning system on noise levels in a surgical ICU before and after its implementation.DESIGNA quality improvement initiative.SETTINGA 12-bedded surgical ICU in a tertiary care university hospital.PATIENTSA total of 148 adult nonintubated and nonsedated patients completed the study, during a 6-week period.INTERVENTIONNoise levels were continuously recorded using a Type II sound level meter for 6 weeks. The study was divided into three phases. The first 2 weeks, baseline noise levels were measured (phase I). In week 3 of the study, a visual noise warning system (SoundEar II) that changed colour depending on noise levels within the ICU was installed and implemented (phase II). The alarm system was set to light up green at levels below 55 dBA, orange at levels between 55 and 60 dBA and red at levels above 60 dBA. The device was switched off at the beginning of week 5 and the sound level meter continued recording noise levels for another 2 weeks (phase III).RESULTSMean night-time noise level was 55.98 dBA in the preintervention phase, 54.14 dB during the intervention, and 54.98 dBA in the postintervention phase. Mean noise level was reduced statistically significantly by 1.35 dBA, and there was a sustained reduction of 0.86 dBA from the baseline noise level 2 weeks after SoundEar II was switched off.CONCLUSIONVisual noise warning systems can be effective in achieving a reduction in noise levels in critical care units.