The Comprehensive Nuclear Test Ban Detection Network, that's usually used to monitor for covert nuclear weapons testing, serves and alternative use in its spare time: it detects asteroid impacts. This video visualises the data it's managed to collect since 2000.
In total, it's helped detect 26 asteroids entering Earth's atmosphere between then and now which have struck Earth, or even just its atmosphere, with at least the energy of one kilotonnes of TNT. Amazingly, that's 10 times as many as we'd expect from existing models of the frequency of asteroid strikes. The largest was, perhaps unsurprisingly, the giant meteor which exploded over Chelyabinsk in 2013. [New Scientist]