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. The detector is powered by a standard 9v battery. PRECISE SIGNALS FOR ACCURACY: This laser receiver features an intuitive interface with optical and acoustic signals that aid in accurate laser plane localization. The LED indicator and beep sounds provide immediate feedback when the laser line is detected. Color: Yellow Material: plastic Package Contents: 1 * Laser Level Only 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.