If used in succession with other protection moves, it has a 50% chance success rate. This will prevent damage and effects of almost all possible attacks that would be inflicted upon the user.
There are a few moves and abilities which do break through this move; Lock On, Mind Reader and No Guard will allow the moves the opponent uses to land on the Pokémon regardless of this move. In addition to that, Thunder & Blizzard have a 30% chance of hitting if used within rain or hail respectively.
The following moves are also unaffected by Protect & Detect; Acupressure, Doom Desire (delayed damage only), Future Sight (delayed damage only), Feint, Imprison, Perish Song, Psych Up, Shadow Force, Transform