deadpix offers two services: bad pixel detection (according to two possible methods), and bad pixel cleaning in which pixels are replaced by an average of their closest neighbours.
The two available methods for bad pixel detection are detailed in the manual page for this command.
Notice that both methods are largely outdated. There are many ways of detecting bad pixels for a given detector, both are now efficient for many reasons. If you want to get a reliable bad pixel map, best is to use a twilight flat-field procedure.