The flash costs of VADs are concerning 0.5 Hz and a pair of Hz. VADs may perhaps consist of a synchronisation operate to reduce the potential of a flash frequency which could result in adverse results, for instance inducing epileptic suits, when devices are in close proximity. Dr Zzeus Q&A: https://www.firesense.co.uk/type/conventional-fire-system/conventional-sounders-vids-vads/