What is the protocol with a mezuzah when someone is injured? Which mezuzahs does that person check just the front door? Side? Bedroom?
Also why would another mezuzah in the home not provide protection to a person if one was pasul?
We do not place a mezuzah on our doors for purposes of protection; we do so because it is a Torah mitzvah. Although many believe that the mezuzah protects inhabitants, its purpose is not protection, and it is incorrect to view the mezuzah as a kind of protective tools.
When things go wrong, some people are eager to check the mezuzos. This is acceptable practice; when things are amiss it is right for a person to check his actions, and the mitzvah of mezuzah, which relates to the houses in which we live, is a good place to start. It is because of this that some authorities reccomend checking mezuzos in times of misfortune.
However, because this is not related to “protection” per se, it is clear that one mezuzah does not help, and somebody wanting to check mezuzos should check all the mezuzos of the house, or at least all the mezuzos that require checking.
For an interesting article on the issue of the mezuzah as protection, please see here.