[fdavison]

The EPA has a website that displays a network of radiation sensors in the US:

https://www.epa.gov/radnet

Hope you never need that information.

[ninjin]

In the immediate aftermath of the 2011 incident at Fukushima Daiichi, a hobbyist network formed around Tokyo monitoring radiation levels and publishing it online. While the act itself was heartwarming, I can very much attest that I never wish a situation where you occasionally refresh an online radiation heat map upon anyone.

[ganzuul]

Expected and wished for a heatmap instead of something quite so... interactive. Good resource nonetheless.

[jdlyga]

I had to track those right after Fukushima, since there were worries about a cloud headed towards the western US.