The Detector pick up a beam when it crosses the electronic sensor window. The detector has 3 buttons:a) OnOff 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:yellow Material:plastic style:Red light The detector is powered by a standard 9v battery. Note: This product is only for Rotary Laser Level 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.