If you have dogs, young children, or irresponsible adults that know how to open a sliding door but not close it, this brilliant, $3.50 DIY is for you.

Hook up a bottle of water or sand to a small pulley with some nylon string, and voila! You've got an automatic sliding door, as the video above demonstrates. Your mileage may vary, naturally, depending on how stubborn your door is at sliding closed.

Still, it's a great time- and effort-saving invention, which might work with other kinds of sliding doors. It was thought up by YouTube user clanmcarthur and shared by his son, Reddit user Defckon .

DIY Automatic Patio Sliding Door | YouTube via Reddit