It locks from outside only... lol but I'm still gonna leave an Allen wrench inside jus in case.... I added a 400 mh on ceiling and 2 8' T12s 110w waist high on wall , still not happy with it, may add another 400 mh , looking for a good mother / veg and cloning room. Veg in one side and clone under over cast on other side, it is only 9 x 9 so it's jus bright everywhere but not as intense , gonna add 2 300w 6500k cfls tom. Once I'm happy I'll hard wire them, till then I'm keeping options open, I got a lil window to get this room right for my needs 3 mothers, I like to veg 60/90 days then they can go to other building/ flower room. 1 1000hps & 5 300w cfls in a 4x8 footprint and a 3x4 closet . The mother /veg room is needed.