Takex's range of speaker sensors are commonly used to provide welcoming messages at building entrances, to protect emergency doors in shopping centres/hospitals/public buildings etc., to deter would-be intruders in security applications, or to trigger alarm/warning messages at construction sites and other hazardous areas. The AV-100E in particular is a horn-type speaker with built-in microphone. A N/O input is required to trigger the playback of your recorded message.