Who cares about the wall? A door handle usually turns down. And even if that thing would turn up the chain would slide down the handle. And even if the handle would pull on the chain the pin wouldn't go out because the chain would pull sideways instead of away from the wall, like the pin needs. And even if the chain just pulled the grenade lose from the flimsy tape the grenade would still just dangle from the chain because you need considerable force to pull out the pin.

Edit: I now realised that it's supposed to pull the pin out when opening the door. Would still need a lot of force.