Everyone at bedikat chametz, including guests who will be there for the holiday, says the kol chamira formula for nullifying any chametz that they own.

One member of each house must search for any chametz (bedikat chametz) on behalf of the entire household. This may be a man, woman, or even a minor child, as long as he or she is sufficiently responsible to conduct the search in all of the details.
 

If you are staying in someone else's house for Passover and the owner is away for the holiday, you must do bedikat chametz for the house--even if the owner has not been there for more than 30 days and even if you will not be eating in that house. The same rule applies for any place that you have rented for any part of Passover and that does not have a resident owner who has done the bedika there.