SBM21 SBM-21 Micro GEIGER Zählerrohr für Beta Gamma Radiometer A-g SBM-10 NEU | eBay
Micod Geiger Detector Driver | PhysicsOpenLab
File:Geiger-tube-sbm20.jpg - Wikimedia Commons
Tubes – PocketMagic
In addition to the Enhanced release of Metro Exodus, I decided to buy my 5th Watch... This one is an LED Matrix strip instead of Nixie tubes. It also has a SBM-21
GQ Electronics Technical Support Forum - Tiny Tube SBM-21