The Model SM900 series is a self-contained, pulse-echo, proximity sensing device that both transmits and receives sonic energy within specified sensing ranges. Operating on 12 to 24 VDC, and employing the latest piezoelectric and microprocessor technology, these sensors detect only those designated objects within a set "window" and ignore all surrounding sonic interference. Prior to operation, a simple and easy push-button "teach" function is used to set the sensing window limits. The near and far limits of a desired sensing window can be set anywhere within the sensing range and may be set to either encompass the full sensing range or be as small as desired. The push-button setup allows a window to be set as small as 2.54 mm (0.10 in ) within the 1 and 2 m ranges and, depending on ambient conditions, a window within the 8 m range can be as small as 102 mm (4.0 in ). A double press of the SETUP push-button makes possible the setting of a default window anywhere within the sensing range.