Nedis ALRMMW20WT motion detector WhiteThis infrared motion sensor wirelessly attaches to a siren so that you always know if someone or something is approaching. The PIR motion sensor is battery operated so you have maximum flexibility over its placement. It has an extensive detection range to ensure you can monitor a wide area for movement. The siren can communicate wirelessly with the sensor up to a distance of 80 metres. Its sound can be heard over the top of the noise of a crowded room