I'm not concerned, for two reasons. First, because the different components of the smoke detectors are manufactured in entirely different plants and are then shipped to where they will be assembled. There is simply no way for contamination to occur to such an extent as you are worried about because the components are never in a situation where that could happen.Now, does anyone seriously believe that these ionization smoke detectors can be manufactured by humans in facilities that are so perfect and pristine that there is absolutely no chance that this "extremely hazardous" americium could contaminate the plastic housing, any other part of the device, or even possibly get on packaging material?
In addition, the americium is itself mixed with gold, which is then plated with layers of gold and silver, to form a small piece of 'foil' that has two 5mm discs cut out that are inserted into the detector casing or circuit board. Alloying the americium with gold virtually assures that a person won't get contaminated, as gold is an extremely malleable metal that is very difficult to fracture by accident. It doesn't shatter into many tiny shards or turn into some sort of powder that can easily be inhaled. It doesn't corrode either, so you don't have to worry about corrosion products containing americium. In a fire the alloy melts, but the temperature is usually too low to boil the alloy or either of its constituent elements, so there is little danger of inhalation. And, assuming that the fire was hot enough to boil the alloy, if you're so close to a boiling piece of this gold-americium foil from a smoke detector to inhale any of it then you're likely in the middle of a massive house fire and are already dead.
You'd have to make a conscious and determined effort to turn these 5mm discs of gold-americium foil into something that could actually harm you. Even eating it wouldn't kill you.