You can keep your child safe around windows with the window safety lock that prevents injury from falls while allowing ventilation. The lock fits both interior and exterior wood windows and slides vertically. Note that children of about four years of age can operate the child safety mechanism. With the window safety lock, you are not only protecting your child from injury due to falls in the home, but you are also taking responsibility for the environment they are growing up in, as the packaging is 100% biodegradable and Cradle to Cradle certified. This means that it breaks down naturally and leaves nothing behind that can harm our planet.