The purpose of Visual Alarm Devices (VADs) is to compliment the audible alarm signal with a visual one. This may be required in areas where people are unable to hear the alarm signal, either due to a hearing disability or local conditions such as high noise levels or the need to wear hearing protection.

With the introduction of the European standard EN 54-23, manufacturers are able to specify visual devices in terms of the range at which the required illumination is met. In the case of EN 54-23, the required illumination is 0.4 lux or 0.4lm/m2.

Three categories of devices are defined, one for ceiling mounted devices, one for wall mounted devices, and an open category. These are tested and assessed by the laboratories of an EU notified body and are then certified as meeting the requirements of EN 54-23, at a specified coverage volume.