In the episode Memory Blank, watch the scene after Danny fights Femalien (The first of three monsters that attack Paulina). When Danny takes out the Specter Deflecter and straps it around Sam's waist, it didn't hurt him. It was shown in previous episodes (e.g. Maternal Instincts) that even when in human form, Danny does get hurt when touching either the belt or someone wearing it. This was also proven later in the episode when Sam, still wearing it, tries to help Danny out of the fountain and he gets shocked.