Trumpy, Radon is bad in some areas, virtually non-existent in other areas. In true American fashion we still have plenty of hucksters trying to scare us everywhere.
A.R., I am not sure if merely monitoring current will really help you much. If these are the small fractional HP fans that I am thinking of they are as likely to fail with a bad bearing as a winding going bad. Some can live with locked rotor. I guess after a while it will blow the thermal fuse but it can run with a seriously degraded output for a long time. If you can live with that, monitoring current should work for you. The other choices are to look at differential air pressure, probably the best solution or to look at shaft RPM like PC fans
