At a recent flea market, someone was selling a surplus military device that was marked as having 900 millicuries and should be disposed of in a safe way. I picked it up to read the words. Whould 900 millicuries be a concerning amount of radiation?
900 mCi is a lot of activity, the problem is that it is impossible to know how bad it will be without knowing which radionuclide is present.
If it is a tritium light with 900 mCi in it, then the external threat is close to zero. Just do not break open the glass vials in a tritium light.
If it is 900 mCi of radium-226 or cobalt-60 then I would suggest to stay a very long way from the object and call the fire brigade or police. They will not have the ability to resolve the problem. What they will do is to seal off the area and then send for expert advice and an emergency team from a nuclear site or some other place where people have experience of working with large amounts of radiaoctivity.
Even a pure beta emitter at 900 mCi is a lot of activity if you are dealing with a high energy beta emitter such as Sr-90 / Y-90.