The Detector pick up a beam when it crosses the electronic sensor window.The detector has 3 buttons:a) On/Off button.b) A Sound button.c) A sensitivity button.This either give a narrow or a broader range of detection.When the detector is too high a slower beep be emitted,when too low, a fast beep be emitted, when same level as beam a continuous pitch sound- at this point the centre of the detector is at the same alignment as .To get accurate results use the spirit bubble to keep the detector level.Colour:yellowMaterial:plasticstyle:Red lightThe detector is powered by a standard 9v battery.Note: This product is only for Rotary Laser LevelPackage Contents:1 * Laser LevelOnly the above package content, other products are not included.Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.