The Detector pick up a beam when it crosses the electronic sensor window.<br> The detector has 3 buttons:a) On/Off button.b) A Sound button.c) A sensitivity button.<br> This either give a narrow or a broader range of detection.When the detector is too high a slower beep be emitted,<br> 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 .<br> To get accurate results use the spirit bubble to keep the detector level.<br> Colour:yellow<br> Material:plastic<br> style:Red light<br> The detector is powered by a standard 9v battery.<br> Note: This product is only for Rotary Laser Level<br> Package Contents:<br> 1 * Laser Level<br> Only the above package content, other products are not included.<br> 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.