This Geiger counter kit uses 2 tubes to provide the ultimate radiation detection device with bright red flashes of light and clicks. Has a switch to select either the super sensitive SBM20 tube which detects beta and gamma rays and gives a background count of 30 per minute or, the other switch position which selects the less sensitive DOB-50 (which has a background count of one or two). The way to use the kit is if the item or area you are measuring overwhelms the sensitivity of the SBM20 tube, operate the switch to measure the amount of radiation as detected by the less sensitive DOB-50 tube. Complete with all electronic parts, Geiger tubes, PC board and instructions. Requires one 9V battery (not included). Size of PC board 2.1" x 4.3". Requires soldering. Skill Level 2.