Ambient radiation is naturally surrounding you at all times, but it’s almost never dangerous. The radiation levels are too low to be a problem. But there are areas where it is higher than normal and potentially-dangerous. Those areas are almost always clearly marked by the country’s government, but it can be fun to see if you can find “hot spots.” To do that, you’ll need a way to measure radiation. Instructables user prabhat_ has a tutorial explaining how to build one of the most feature-packed Geiger counters we’ve ever seen.
