The only definitive way to find out the status of any patent is through litigation: "The [US] PTO grants most patent applications, then lets people fight over

The only definitive way to find out the status of any patent is through litigation: "The [US] PTO grants most patent applications, then lets people fight over their validity later on. ... Almost half of patents litigated to judgement are invalidated; of those found valid, half are found not to be infringed." [1] 1. Michael Heller, The Gridlock Economy, p. 53