The FireAngel W2-LFS-630-EUT low frequency siren is an additional addition to the FireAngel smoke, heat and carbon monoxide alarm. You link the low frequency siren to all FireAngel products. Connect the siren to your mains power and let the products communicate wirelessly with each other. A low frequency siren is good for the hearing impaired. Some tones of a regular alarm do not belong to people with bad hearing. A low frequency siren, on the other hand, often does.